I agree with parts of everyones posts above. First you should give a try to turn him from the dark side. It's evident that you must have some affection for the boy or you wouldn't be in the woods with him. This also makes you the prime person to try to save him.

If he doesn't listen then get as far away from him as possible or he may just drag you down with him. After all, who was helping him in the woods? At this point turning him in would not be out of line.

Good luck, This is a hard situation.