According to Snopes.com, the story is false.

Snopes has discovered claims of the game started back in April, after The Daily Mail published a case in which a 13-year-old girl was missing.  But digging deeper, the original article, cited by The Daily Mail, stated that the "game" was probably a hoax and that police were not able to find any trace of a real plot, only shares from panicked parents. "The Daily Mail" made no mention of the, in Snope's words, urban legend aspect.

But as Snopes found out, there is no evidence that the game is real and that kids are actually taking part.