Last sighting of runaway Hannah

Watch Hannah's last recorded movements here

Hannah was claiming she was 16 in her chatroom messages which is of particular concern to the police. Her parents James and Lilla May, from Tillingham near Burnham, said she has never done anything like this before and are beside themselves with worry. Mr Cooper, 53, added: "She had mentioned she had an Italian penpal, his anglicised name is Josh. I think he says he's about 14 or 15 years old but I doubt it. She met him through a website and has known him for some time. It looks like he has flown into Stansted and she has gone to meet him."

Hannah is 5ft 4in, slim, with long black curly hair. She was wearing a light-coloured jacket, jeans and black boots.

At about 11am on Sunday Hannah cycled two miles from her home to the station in Southminster after telling her parents she was going to meet a friend in her village.

Her gold-coloured mountain bike was found later at the station. Her parents raised the alarm within 90 minutes.

The CCTV footage shows Hannah on the 12:05 Southminster to Wickford service.

She caught the 12:39 from Wickford to Liverpool Street, arriving in London at 1.20pm.

Hannah, a talented musician who hoped to be a forensic scientist, is thought to have taken clothes and toiletries but only has about £25 and does not have her passport.

The Coopers have been calling their daughter's phone since she vanished but it has been switched off. They have put an extra £20 of credit on the phone so she can contact them.

The family's computer is being examined by police experts to see who Hannah was talking to online and her school friends have been interviewed by police.

Hannah had received a euro through the post from "Josh" who told her to start saving for his arrival in England.

Mrs Cooper, 49, who also has a 17-year-old daughter, Amy, said: "When they saw her on the CCTV they said she was walking confidently, like she knew where she was going.

"She's not streetwise but she's capable of dealing with situations. She has a very good sense of humour, we are very close. I'm confused as to how she could do this to us."

Mrs Cooper added: "She spent too much time on the computer but I always made sure she was off by 10pm or 10.30pm.

"She wanted to have one in her bedroom but I wouldn't allow it. It's difficult with children how much freedom you give them. Especially living here - they feel isolated. But you can't mollycoddle them all the time."

Mr Cooper said: "I want her to know we love her and she's not in any trouble, we just want her to come home." A police spokesman said: "She has said she is older than she is and obviously any teenager of that age who is suggesting they are older is a concern to us.

"Our concerns are she is not streetwise and she's very au fait with using the internet and could potentially get herself into trouble.

"Police are talking to friends and family and looking at a raft of information from her computer. Hannah has no travel documentation that would allow her to leave the country so a likely scenario at this stage is that she met someone off a plane at the airport."

A police spokeswoman appealed to hoteliers and guesthouse owners to get in touch if they believe they have seen Hannah.

"We are particularly appealing to any hoteliers or owners of bed and breakfast accommodation, either in Essex or London, to report sightings of Hannah," she said. "It is a strong possibility she is now in the company of someone else."

Senior investigating officer Detective Superintendent Keith Garnish said: "It is very worrying that Hannah travelled to London after telling her parents that she was going to visit a friend. Hannah has never gone missing before and we are particularly concerned about her due to her age and the fact that she looks much older.

"Her parents want to tell Hannah that they really want her back home safe and well and that she's not in any trouble for going missing."

Anyone with information should contact police on 01245 491212 or ring Crimestoppers on 0800 555 111.