Police are searching for a 14-year-old girl who they believe has disappeared with a 35-year-old man.
Schoolgirl Lorna Vickerage, from Doncaster, is thought to be with John Bush, also from Doncaster, South Yorkshire Police said. A spokesman said: "Lorna and John are thought to have been in the Highfields area over the last two days.
"Lorna was last seen at 2.30pm on Monday June 10 at Outwood Academy in Adwick wearing her school uniform but it is unlikely that she will still be wearing this."
Police said they are both known to frequent the Askern, Adwick, Woodlands and Highfield areas of Doncaster.
Miss Vickerage is described as white, slim build, about 5'4", with long straight, thick blonde hair, while Mr Bush is described as white, stocky build with receding dark blonde hair.
South Yorkshire Police are asking anyone with any information on their whereabouts to call South Yorkshire Police on 101 quoting incident 609 of June 10, 2013.
Detective Chief Inspector Craig Robinson of South Yorkshire Police said Bush has a history of fraud but police are unclear about his motives for disappearing with Lorna.
Speaking at a press conference at Doncaster Police Station this morning, he said: "The last positive sighting of Lorna was with John Bush, and that was at 10.15 yesterday morning in the Highfields area of Doncaster.
"At that time she was introduced to a local couple by John as his daughter. Lorna appeared to be safe and well and chatty."
Mr Robinson described Lorna as "quite vulnerable" and said she was in the care of the local authority and put in foster care on Friday.
He said Bush, who was a family friend for "some time", is a single man with no family who has no history of similar offences, although he does have a fraud conviction.
"What does concern me is he's a liar, he's a fraud, he's a cheat and it's what he's telling Lorna," Mr Robinson added.
He said Bush was believed to be pretending Lorna was his daughter "as a guise" to avoid suspicion.
The force helicopter was scrambled yesterday to help with the search and police are trying to trace the vehicle Bush was in - a silver Ford Mondeo.
Mr Robinson said: "Lorna, you're not in trouble. Your mum's petrified, she's worried to death, we're concerned for your safety. We don't know why you've gone with John and we don't know why John's taken you.
"Let us know you're safe and well. Speak to John - tell him to hand himself in, and if you're listening, John, we really do need to speak to you. The sooner you get this over with, the better."
Lorna's mother Christine, 36, wrote on Facebook today: "my baby plz come home darling we love u so much".
Alongside a picture of her daughter, she posted: "this is my gawgess lovin daughter if anyone as any idea were she could be would u plz contact me I just want her home safe thankyou".
She said: "come home my baby girl iam so worried plz just ring me we all love u so much".
Bush was described as a "professional fraudster" by a judge who gave him a 14-month prison sentence suspended for two years earlier this year on condition that he does 200 hours of unpaid work.
York Crown Court heard how he committed a range of frauds including persuading garages to give him courtesy cars he never returned and using a holiday cottage without paying.
The judge was told he has a number of convictions for dishonesty.