Lost Boys by Orson Scott Card

For Step Fletcher, his pregnant wife DeAnne, and their three children, the move to tiny Steuben, North Carolina, offers new hope and a new beginning. But from the first, eight-year-old Stevie's life there is an unending parade of misery and disaster.

Cruelly ostracized at his school, Stevie retreats further and further into himself -- and into a strange computer game and a group of imaginary friends.

But there is something eerie about his loyal, invisible new playmates: each shares the name of a child who has recently vanished from the sleepy Southern town. And terror grows for Step and DeAnne as the truth slowly unfolds. For their son has found something savagely evil ... and it's coming for Stevie next.