Detectives who ran the Sarah Payne inquiry today joined the search for missing ten-year-olds Holly Wells and Jessica Chapman.

Cambridgeshire Police say the move does not mean they believe the girls have been abducted. They say the disappearances are being treated as a missing persons inquiry.

Officers have received more than 1,500 calls about the girls since they were reported missing on Sunday evening, including several reported sightings.

And yesterday the youngsters' favourite footballer David Beckham - and his Manchester United team-mates - made a personal appeal for the pair to return home.

Police described the possible sightings of the girls as "extremely encouraging" but said they were keen to seek advice from the Sarah Payne team.

Eight-year-old Sarah went missing for 17 days after she vanished from a field near her grandparents' home in Kingston Gorse, East Preston, in July 2000. Her body was eventually discovered in a shallow grave near Pulborough.

Detective Superintendent Alan Ladley, who led the search for the missing girl and the eventual murder hunt, said he was reminded of the tragedy of Sarah's murder every time he heard of youngsters disappearing.

He said: "In a case like this we like to share any assistance we can, just as we did with Milly Dowler.

"We learned an awful lot in the search for Sarah and it may be that we can offer some ideas and help in this case.

"The hope is that they have just wandered off and are safe, and they are treating this as a missing persons inquiry, but professionally you can't ignore the possibility that it is something more sinister."

Mr Ladley will be accompanied by Detective Chief Inspector Tosh Underhill, another veteran of the Sarah Payne inquiry.

Detective Superintendent David Hankins, a senior officer in the hunt, said police were grateful for Manchester United's help and that of the Sarah Payne detectives.

He said police were sifting through reported sightings but said one - in Little Thetford, eight miles from their homes in Soham - matched the girls "to a T".

Police are continuing to examine computers from the homes of girls, who are said to have enjoyed sending e-mails, and want to know if they arranged to meet anybody via the internet.

Mr Hankins said a reported possible sighting of the girls, said to be clean, dry, happy and healthy, meant police could not rule out the possibility that they were staying with someone.

But he said police fears for the safety of the girls were being "raised by the hour" and officers would today begin searching waterways.

He said: "We are increasingly having to look at the possibility that the girls have been abducted and that this will be a criminal investigation."

Calling in Sussex Police officers from the Sarah Payne inquiry had been "the most harrowing thing imaginable for the family", he said.

He added: "We have got our fingers crossed and hope and pray that the girls are somewhere safe but we have got to be realistic.

"We have to look at the possibility that they have not been seen for three days and could have been abducted."