Police fear a 13-year-old girl who has gone missing from her home in Hull may be with a man she met on the internet.
Hayley Foster was last seen at 1045 GMT on Friday when she told her parents she was going on holiday with friends.
But her family raised the alarm after they discovered the trip was false and friends revealed she was in possession of a train ticket to London.
Police say Hayley may have arranged to meet a man calling himself "Simon" who says he has a 15-year-old son.
Officers are treating her disappearance as an urgent missing persons inquiry and are working closely with colleagues in London.
Computer equipment has been taken from her house to look for clues on where she might be.
Hayley is described as white, 5ft 2ins tall with a pale complexion and shoulder length blonde/ginger hair.
She was last seen wearing a sandy-coloured jacket, black pinstripe trousers and white and pink Reebok trainers.
Inspector Steve Page, of Humberside Police, said: "It is very important that we trace Hayley as soon as possible.
"We are almost certain that she is in the capital. Hayley needs to be with the family who can best cater for her needs and look after her.
"I would urge anyone with information about Hayley's whereabouts to contact us as soon as possible."
Anyone who thinks they may have seen her is asked to contact detectives in Hull or their nearest local police station.