Son of the Mob by Gordon Korman

His father is the mob boss that her father is out to catch!

Tenderness by Robert Cormier

Eric, just released from juvenile detention, is looking for tenderness - in the company of innocent girls.

Acceleration by Graham McNamee

Duncan finds a little leather book - a diary of "a serial killer stalking his prey in the subway . .... What would you do with a book like that?" (From the jacket)