The Boy from the Woods (Wide 01) by Harlan Coben

In the shocking new thriller from the #1 New York Times bestselling author of Run Away, a man whose past is shrouded in mystery must find a missing teenage girl before her disappearance brings about disastrous consequences for her community . . . and the world.
The man known as Wilde is a mystery to everyone, including himself.Decades ago, he was found as a boy living feral in the woods, with no memory of his past. After the police concluded an exhaustive hunt for the child's family, which was never found, he was turned over to the foster system.
Now, thirty years later, Wilde still doesn't know where he comes from, and he's back living in the woods on the outskirts of town, content to be an outcast, comfortable only outdoors, preferably alone, and with few deep connections to other people.
When a local girl goes missing, famous TV lawyer Hester Crimstein—with whom Wilde shares a tragic connection—asks him to use his unique skills...