The hunt for Amanda Dowler, the missing Surrey schoolgirl, is likely to be scaled down amid growing concern about the expense of the £1m inquiry and the lack of a breakthrough.

Police believe the 14-year-old girl, known as Milly, is probably dead and have even investigated the possibility that she has committed suicide and that her body remains undiscovered.

The teenager disappeared as she walked home from school in Walton-on-Thames on 21 March.

Police are about to make a new appeal for help in finding Milly, but unless they receive a significant lead in the near future it is understood that officers will be taken off the 100-strong inquiry team. Surrey Police last night denied that it had any firm plans to scale down the inquiry.

Despite nationwide publicity, the police have no idea about the whereabouts of Milly. They have warned her parents, Sally and Robert, that she is most probably dead, but do not know whether she has been abducted, has run away or killed herself. All the main lines of inquiry have been exhausted and Surrey Police has become increasingly alarmed at the rising cost of the investigation, which is understood to have exceeded £1m. The investigation remains a missing-persons inquiry and police managers are worried that the case is draining their finances.

At first the police thought that Milly had almost certainly been abducted, but when there was no evidence of a street kidnap they switched to the possibility that she had run away with a man she had met via the internet. They have considered other explanations, including suicide.

Two men have been questioned about Milly's disappearance, but both were released without charge.

A statement issued earlier this month by Surrey Police said: "It is an extremely unusual incident for a girl to go missing without a single clue or lead to help the investigation team."

A spokeswoman for the force said yesterday: "We have not got any plans to scale down the inquiry at the moment."