From today the vans will carry a poster of Sasha McLeish, 15, who went missing in June, in the hope of tracking her down and returning her to her family.

She is one of the thousands of children who disappear from their homes every year. Speed is critical in locating missing children and campaigners say that the swift circulation of a child’s picture can make the difference between a fast recovery and a prolonged search.

It is thought that America offers a salutary example that could help missing children to be tracked down: the US has for years used pictures on milk cartons to publicise missing children, changing the pictures regularly to report new cases.

The missing children in the British campaign will change every month. Scotland Yard’s missing persons bureau will select the cases and EMCOR, a US company that services Heathrow, will supply the posters and the vans. For the Sasha McLeish campaign EMCOR staff will also carry car stickers with Sasha’s picture and a police free phone number.

Many of the children who disappear in Britain end up begging, stealing or in prostitution. Although a large number are found quickly or return home by themselves, some never reappear.

Frank MacInnis, chairman of EMCOR, said that a similar campaign in the US had been a success. “So far 28 of the 100 children in our US campaign have been found, which the National Centre for Missing and Exploited Children says is a very good result.”

Sasha McLeish, of Luton, was last seen by her mother on the morning of Friday, June 23. She had stayed with friends the previous night after decorating her church for a wedding and came home to get ready for school. Her mother, Avril Clarke, said yesterday that she was happy and excited, and nothing was out of the ordinary. “We didn’t talk for long that morning because she was a bit late for school . . . She asked if she could go to a dancing class after schools and then on with some friends afterwards. In the end I said fine. She never came home.”

Sasha went to school and on to a fair with her friends. They last saw her as she set off for home at about 10pm. She was in her blue school uniform.

Mrs Clarke said: “It has been a horrible nightmare since that day. Her brother and sister have taken it very hard . . . I cannot understand why this has happened. I just want to tell her to come home, ring me or anything. You are not in trouble.”

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