Kill for me / Karen Rose.

Enhanced descriptions from Syndetics:

Five teenage girls have been viciously attacked. One survived. Only she can reveal the secrets of a disturbing ring of people who kidnap and sell teenage girls on the black market. But those responsible for the crimes will do whatever it takes to maintain her silence. Susannah Vartanian and Luke Papadopoulos have both sworn to stop the murderers for their own personal reasons. The investigation leads them to the shady realm of Internet chat rooms, where anyone can mask his or her identity. They soon discover a chain of deception so intricate they don't know whom to trust. Finding comfort in each other's arms, they begin to unravel the intricately knotted threads, but the killers are ruthless and determined, and won't hesitate to take extreme measures to insure their anonymity and keep their business intact. When Susannah proves to be inexplicably linked to the crimes, her life is soon in danger, and Luke will do everything he can to save the woman he loves.