Hold Tight - Harlan Coben

Tia and Mike Baye never imagined they'd become the type of overprotective parents who spy on their kids. But their 16-year-old son Adam has been unusually distant lately, and after the suicide of his classmate Spencer, they can't help but worry. They install a sophisticated spy program on Adam's computer, and within days they are jolted by a message from an unknown correspondent addressed to their son: 'Just stay quiet and all safe.' Meanwhile, browsing through an online memorial for Spencer, Betsy Hill is struck by a photo that appears to have been taken on the night of her son's death and he wasn't alone. She thinks it is Adam Baye standing just outside the camera's range, but when Adam goes missing, it soon becomes clear that something deep and sinister has infected their community...