Fears were growing last night for the safety of two missing girls who may have gone to meet someone they contacted on an internet chat site.

Police said they were concerned about Denise Robotham, 12, and Sinead Ormand, 13, after they left their north London homes for a 'teenage adventure' on Friday afternoon and failed to return home.

Scotland Yard said the girls had been in contact with a number of people online, and police were last night investigating email addresses found on Sinead's computer. They have already identified three 14-year-old boys in Norfolk. The girls had invited themselves to Norfolk but the boys said they had asked them not to come. The boys denied that Denise and Sinead had been to their homes.

Police said that the pair left their school, Hornsey School for Girls, in north London on Friday after attending the first two lessons of the morning. They believe they went to Sinead's house in north London, to collect belongings and money. Denise was also spotted by a neighbour returning to her home and leaving shortly afterwards.

Denise is described as black, 5ft 7in tall with long hair tied back in braids, with bleached tips. She was wearing her school uniform when she left school, but police believe that she took spare clothes with her and may be wearing a red jacket. Sinead is described as white, the same height as Denise, with shoulder-length blonde hair. She was also last seen wearing her school uniform.She may be wearing a three-quarter- length cream jacket.

The girls are thought to have around £100 between them, a tent and spare clothes. They did not take their mobile phones.

The investigation already involves three police forces led by the Metropolitan Police. British Transport Police are examining CCTV footage of mainline train stations across London, while Norfolk Police are conducting local inquiries.

Detective Inspector Paul Davidson from Tottenham CID said: 'There is no evidence at this stage to suggest they have fallen into danger. However, due to their age, lack of recent sightings and the impending cold weather we are very keen to trace them as soon as possible.

'Our initial inquiries have confirmed they were in contact with people over the Internet. However we do not know whether they went to meet one of these people. We are speaking to their friends to see if they can shed any further light on the girls intentions.'

John Carr, internet adviser to the children's charity NCH, said: 'We can only hope and pray that they return safely. But whatever the outcome this demonstrates the dangers of meeting people from internet chatrooms. These girls had no idea that the person they were talking to was 14 or 40.'