The additional picture adorning this piece is not my good self after a much-needed makeover, but is of a friend of mine. His name is Alan Templeton. He's a very bright, engaging, gregarious young man, the son of a couple I've known for years. Let me tell you about them first, and then I'll come back to Alan.

In the late 1960s, when I was a long-haired student at New College, Edinburgh, one of my tutors in the New Testament honours class was Dr Douglas Templeton. With his crumpled kilt and big dog, he looked more like a Big Issue seller than a corporate man. A brilliant postgrad student at Tubingen University, Douglas was a superb teacher. I well remember surreal seminars in his Rose Street flat, involving St Paul, two incomprehensible German theologians and a crate of beer.

A fellow student in my year, Elizabeth Maclaren, had an outstanding philosophical and theological mind. After graduation, she became a lecturer in divinity at New College. She and Douglas married, and Liz gave up full-time academic work to look after their three children, Kirsten, Alan and Calum, producing highly regarded theological work from her home base.

On visits to their family home, I met Alan. Our talk was not of theology, but of football. He graduated from the University of Wales, dreaming of a career in documentary film-making. Then, on November 25 last year, 24-year-old Alan suddenly went missing. He had no passport with him. His mobile phone remains switched off. There has been no activity in his bank account. Douglas and Elizabeth, who live near Pitlochry, still have no idea whether he is alive or dead. They live in limbo.

As has been fully reported in The Herald, 21-year-old Iain Nicholson from Bearsden went missing on February 2 this year. Despite appeals on television and posters in various places, his anxious family still wait for news. Every ring of the telephone triggers both hope and a sense of dread. Alan and Iain are part of a shadowy moving mass of missing people in this country. Home Office statistics released in 2000 show 210,000 people were reported as missing. The National Missing Persons Helpline says that men in their twenties are most likely to disappear.

The reasons why people suddenly go AWOL vary; some fall out with their family, others want to reinvent themselves in a new location; others again have mental health or addiction problems. If an adult wishes to go to ground, he or she has every right to do so. When no offence has been committed, overstretched police cannot search for every person who has left home without explanation.

Alan Templeton had been working in France, and a relationship he was in had broken up. The outgoing young man with a normally sunny disposition had been depressed.

His sister, Kirsten, who works with Morgan Stanley financiers in Paris, and brother, Calum, a physics student at Cambridge, believe Alan is still alive, but are worried by the lack of contact. It's not like him, they say.

Every single case of disappearance brings heartache. I should know. More than 30 years ago, my elder sister, Mary, vanished from her home in the Dumfries area. She had been troubled and depressed, especially after the death of my mother. She left a husband and three young children. All traces were covered up. Letters to possible addresses were returned as "addressee unknown". No member of the family has heard from her since.

Is she still alive? If so, does she live in this country or abroad? Has she got a new name? Could that face in the crowd be her? When someone disappears in mysterious circumstances, worry, guilt, fear and feelings of rejection, anger and despair all surface at different times. Possible sightings bring anxious elation, followed by sadness and resignation. Birthdays and anniversaries are particularly difficult. Births, marriages and deaths of family members are haunted by a ghost at the feast. What families want most of all is a message from the vanished one, a message which says that he or she is alive and well. When only the sound of silence is heard, hearts remain heavy.

My dear friends Douglas and Liz Templeton, like all loving parents, simply want to know if their boy is alive. If anyone thinks they may have seen Alan - he is 6ft 4in tall, and has short brown hair, brown eyes and a fair complexion - please contact the National Missing Persons Helpline on 0500 700 700.

If Alan gets sight of this and doesn't yet feel able, for any reason, to be in direct touch with his parents, he can call me.

One short call can end the heartache, can soothe the fears, can allow sleep to be a welcome nocturnal guest once more.