The parents of missing teenager Amanda Dowler yesterday made a tearful public appeal three days after she vanished without trace.

In a cruel twist, police later found a body on a railway line near the 13-year-old's Surrey home - but it turned out to be that of a man believed to have committed suicide.

British Transport Police said his death was, at this stage, unconnected to the search for Amanda, known as Milly to her family.

Meanwhile, her distraught parents, who were informed of the find by a police family liaison officer, were keeping an agonising vigil at their home in the village of Walton Park, near Hersham, Surrey.

Earlier, they told a news conference organised by Surrey Police they were "numb" with worry, and that it was out of character for Milly to go anywhere without letting them know.

Robert Dowler, 50, an IT consultant, said: "Someone, somewhere, must know something."

His wife, Sally, 42, said: "We're just so desperately worried. Please, please give her back to us."

Police have broadened their search for the girl, with 100 officers on foot and a helicopter scouring the area.

Milly disappeared on Thursday after leaving Heathside school in Weybridge, where her mother is a teacher, with a group of friends.

They caught a train to Walton-on-Thames, visited the Travellers Cafe where they bought some chips, and then set off home separately.

Milly took the mile-long walk home from Walton-on-Thames train station and was last seen heading towards her home in Walton Park.

Mr Dowler thanked local residents who have put up missing person posters of Milly, and said: "We've been absolutely overwhelmed by everybody's help and support.

"It's my wife's birthday this week. It would be the best present in the world if we got Milly home safe."

Asked if they were still hopeful their daughter was alive, Mrs Dowler fought back tears and said: "We just desperately hope she is."