Hold tight by Harlan Coben

Kids in peril lie at the heart of Harlan Coben's Hold Tight, which twists and turns while exploring fierce parental love. A doctor, having installed spyware on his son's computer, finds that he is somehow involved in the suicide of his friend.

Synopsis by Foyles.co.uk

Tia and Mike Baye never imagined they'd become the type of overprotective parents who spy on their kids. But their sixteen-year-old son Adam has been unusually distant lately, and after the suicide of his classmate Spencer Hill - the latest in a string of issues at school - 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...