Police say Nobantu Zani, whose decomposed body was found covered with branches on moors near Bingley, West Yorkshire, may have led a double life.
Nobantu, who liked to be known as Mandy, had not been reported missing because her South African mother thought she was staying with a friend.
The teenager had not been seen since 11 September and police believe she was strangled soon after that date - with her own chiffon scarf.
Mandy regularly played truant from Buttershaw Upper School in Bradford, and had not been seen at home since 9 September. Her family have no idea where she had been staying.
Police believe her friends could hold vital clues to her death, and her closest friend has been asked to draw up a list of people who may be able to shed light on her life away from school.
Detective Superintendent Tony Whittle, leading the inquiry, said: "It may be that she was living some kind of double life. Her mother, until we spoke to her, had no idea that anything untoward had happened."Reuse content