The English-speaking teenager who turned up in Berlin claiming to have lived in a forest for the past five years has refused to make a public appeal.
The boy's reluctance has frustrated German police who had hoped it could lead to his identity being discovered.
"There is no one to appeal to -- all my family are dead," he told the legal guardian appointed to look after his interests.
Initial investigations by police and Interpol have failed to shed light on the identity of the blond, blue-eyed boy known only as Ray, who says he remembers few details about his life.
Police had hoped the guardian would allow a photograph of the boy to be released in an appeal for information. They also hoped that linguistic analysis, DNA sampling or dental records might provide clues to his identity.
However, the boy has, so far, refused all offers to help him discover his history and have his photograph published. Instead, he wants "to be left to get on with his life".
A spokesman for the police confirmed that a legal guardian, a female social worker, had been appointed by the family court on Monday afternoon, but that the move had so far failed to unlock the investigation.
Thomas Neuendorf, of the Berlin Police, said: "The boy said that his father had told him that there were no relatives, save his parents. The boy said that since both parents were dead, there was no family to appeal to."
Mr Neuendorf added: "We've asked the guardian to speak to the boy again to try to change his mind. At this point, a worldwide public appeal may be the only way we will ever discover who he really is."
The boy has told police that he and his father, Ryan, had lived in the forest since the death of his mother, Doreen, in a car crash about five years ago.
He said he walked north when his father died in a fall in the woods. He turned up, two weeks later, at Berlin City Hall on September 5 to ask for help. (© Daily Telegraph, London)