A child's life is full of milestones: first steps, first tooth, birthdays, going to school. We celebrate their anniversaries with presents, balloons, cake and funny hats. But how do you mark the anniversary of a child's apparent evaporation into thin air? So much has happened since the news flash on May 3 last year revealing that a three-year old girl had disappeared from her bed in the Portuguese resort of Praia da Luz: a new prime minister, an attempted bomb attack on Glasgow Airport, oil selling at $120 a barrel, the credit crunch. But Madeleine McCann's parents, Kate and Gerry, must feel as if they are witnessing these events through frosted glass. Now in Praia da Luz, the day has arrived that they have dreaded.

They prepared as best they could by using it to highlight their campaign for a Europe-wide "amber alert" system for children who go missing and launching what they admit is probably the last big push for information about their daughter. But first they needed to reclaim themselves as people.

As Gerry told radio listeners this week: "We're not characters in a soap opera." It was a timely reminder because throughout their ordeal, there has been a tendency to treat this couple as if they weren't real people. To some extent they unwittingly conspired in this because of their desperation to keep Madeleine's image and details in the public eye in the days and weeks after her abduction.

A network of friends and relatives, including Gerry's family in the West of Scotland, used the press and the amplifying power of the internet to reach into our lives in the way an old-fashioned poster campaign never could. (In 1991 when the British toddler, Ben Needham disappeared from the Greek Island of Kos, the story quickly faded from public consciousness.) This time around, that haunting video image of this pretty, dimpled little girl turning her uncannily knowing gaze on the camera is imprinted on tens of millions of memories, far beyond Portugal. The McCanns' publicity machine turned out a succession of smiling sunlit portraits. Madeleine soon became "Maddie", as if she was the wee girl next door to all of us.

The public response was so huge that newspapers noticed a spike in their sales each time a new picture appeared on their front page. The level of interest paralleled the public gush of emotion following the death of Princess Diana. There was an almost predatory element in this that some of us found distasteful. It's no coincidence that Diana Spencer and Kate McCann share a number of features: both blonde, willowy and photogenic. With her solidly Scottish husband at her side, the daintily pretty, fragile-seeming Kate was a shoo-in for celebrity status.

There is something mawkish and voyeuristic about the way thousands of ordinary people they had never met seemed to relish bit-parts in these terrible human dramas, whether it is leaving flowers and tear-stained notes at Buckingham Palace or distributing "Find Maddie" posters and wrist bands. Through most of the summer, the McCanns were able to ride this wave of sympathy in a way that even before her arrest, the lumpen, hapless Karen Matthews, was never able to do. Soon celebrities were queuing up to do their bit. David Beckham, Christiano Ronaldo and Johnny Wilkinson were all willing recruits to the cause.

However, all the while, the McCanns themselves were becoming commodified by this media circus. There was always a slight double-edge to the publicity.

From the beginning they have had to cope with the accusation that they should never have left Madeleine and twins, Amelie and Sean, asleep in the apartment while they joined their friends at a Tapas bar 50 metres away. In a two-hour television documentary about the case shown last week, the McCanns ate a lot more humble pie about this than they appeared prepared to do at the time. As Kate put it: "We have to live with the fact that if we'd been there, then possibly, probably, it wouldn't have happened."

One suspects that the reason this case touches parents so deeply and painfully, the reason why so many of us can't look at images of Madeleine, yet can't look away either, is simple: she could have been our child. Gerry McCann told viewers: "People say they've never done that and you know, who am I to argue?" Of course, he doesn't mean it. Let's be honest: which one of us, exhausted after a day's relentless caring for one or several small children, hasn't done something unwise, made some oversight, fallen prey to some distraction that induces a retrospective shiver. And what's the difference between us and the McCanns? Simply this: we got away with it.

Nobody disappeared, nobody died and nobody found out. Thank God.

Some of the initial criticism over this issue came from the Portuguese press and resulted from a culture clash. Many British tourists are horrified at the way small whining children in Mediterranean countries stay up late at night, long after their own have been fed, watered, bathed and tucked up in bed, a practice Continental parents regard with equal disapproval.

In retrospect, it was inevitable that having turned on the publicity tap so effectively, the McCanns would discover that they had little control over what came out of it. Eventually, what came out was bile. Those wanting to find fault with the McCanns were quick to pick on their public demeanour: Gerry seemed too briskly efficient, his wife too stoically brittle. (Some even attacked her for wearing clean, pretty clothes and combing her hair!) Above all, where were the floods of tears we've learned to expect in such cases? This turns out to have been a deliberate ploy, a measure of their determination to subjugate everything to their quest for their child. In last week's documentary, we revisit the press conference where Kate McCann held up pyjamas like Madeleine's. It emerges that immediately before and afterwards she had been locked in the toilet in floods of tears but a behavioural psychologist had advised her not to cry in public because of the perverse pleasure it might afford to the abductor.

Just when things looked as if they couldn't get worse, they did. Like a Greek tragedy, one misfortune piled upon another. The Portuguese police, unable to find any definite lead and apparently more desperate to nail someone for the crime rather than find Madeleine, named Gerry and Kate McCann as "arguidos" in August. This had the effect of declaring open season on the McCanns in the Portuguese press. Some of the large British press pack still kicking their heels in Praia de Luz, desperate for new story angles, took the lazy route and lifted every wild theory and allegation from the Portuguese media. Over the following months, Express newspapers in particular, fed freely on these stories, alleging the McCanns were implicated in their daughter's death without a shred of supporting evidence.

The McCanns' libel lawyer later said he had never come across a more clear-cut example of defamation. The couple sued and won front-page apologies and £550,000 in damages to bolster the Find Madeleine fund. What riles more responsible newspapers about this case is the questions it has raised about a self-policing media, especially when Peter Hill, editor of the Express, continues to sit on the Press Complaints Commission.

Unfortunately, the McCanns have no way of defending themselves against the nasty underbelly of society whose poisoned accusations have been breeding in the blogosphere. The couple's careful cataloguing of the mountain of correspondence they have received includes boxes devoted to the nasty and the nutty. One venomous Christmas card read: "Your brat is dead because of your drunken arrogance." Because of their on-going arguido status and the way the Portuguese legal system works, the McCanns are unable to counter much of the tide of misinformation that sometimes threatens to overwhelm them. Besides, they regard it as a dangerous distraction from their only goal: finding Madeleine.

She is probably now the most famous child in the world. Billions of pictures have been printed and trillions of words written since May 3, 2007, but nobody can find her. "Sightings" in Morocco and France came to nothing. An artist's sketch of the man with straggly hair and drooping moustache they believe carried Madeleine away has failed to flush him out.

The story of Madeleine continues to have a beginning but no end. The McCanns continue to talk of her in the present tense. "She is four years old," Kate resolutely told Members of the European Parliament recently. (She was three when she disappeared, the same age as her younger sister, Amelie, today.) Part of the problem for the McCanns was the way they were plunged into a legal system they didn't understand. Some of the comment in the British press about their handling of the case has been overtly xenophobic. This is not to deny that parts of the investigation were flawed: the length of time taken to arrive at the apartment, the failure to carry out immediate forensic tests or seal off the resort. Inevitably it raises the question of whether the British police would have done better. The Shannon Matthews case suggests perhaps not.

Could press, public and police form a more effective partnership in these cases? The McCanns believe they could if Europe adopted the well-tried "amber alert" system used in the US, which has resulted in 68 abducted children being returned. When Madeleine disappeared, it was the McCanns' friends, not the police, who suggested roadblocks on the motorway leading to the Spanish border.

Although it's almost impossible to believe anything good coming out of this story, beyond the (surely now remote) possibility of the child's safe return, a Europe-wide system that would quickly disseminate images and details of an abducted child is surely worth fighting for? In Britain, a Child Rescue Alert system launched in 2006 has been used only three times and wasn't activated after the disappearance of Shannon Matthews. Part of the virtue of the American system has been its deterrent effect. Yet the McCanns have so far secured barely a third of the support they need from MEPs to bring amber alerts to Europe. And while the American bureau for tracking missing children has a budget of £20m a year, the equivalent British charity struggles along on £300,000.

The worst thought on this dark anniversary is that the McCanns' torment could go on for years. Winnie Johnson, the tragic mother of Moors murderers' victim Keith Bennett, left her back door on the snib every night for the rest of her life "just in case". Hope may never die but the ordeal takes a heavy toll. Kate McCann's stiff jaw and lined face are a reminder of the ageing effect of stress. The worst thought today is that on May 3 next year and the year after, they could still be watching and waiting for Madeleine and every Friday the Lady of Our Light Church in Praia de Luz will still be holding candlelit vigils for her.

We need to remind ourselves that the McCanns are real people and this is not some dark fairy story. There is a child in this story but it is not a children's story, real life, not fantasy. It is a story about an empty bed but not one from which a child can evaporate into thin air. Someone, somewhere knows where she is.