The Boy from the Woods by Dean Harlan Coben 

A boy called Wilde, who seemed to be raised wild in the woods as a child, is now a security expert who still lives alone, off the grid.  A neighbor's daughter has disappeared and Wilde is asked to find her.  He's good and he does find that she never disappeared, but that her 'father' helped her to hide in his basement.  Turns out she was trying to 'fit in' with the cool kids at school by trying to succeed at a challenge.  Then the boy who picked on her the most goes missing and he's the son of a media mogul.  Now it's Wilde who is tracked by the security team that is supposed to have kept the boy from disappearing, and this time it's a kidnapping.