To all worried parents only!!! my buddy has a underaged teen daughter who is very ually promiscuous.?

She gets her so called dates thru the internet and sites and disappears for hours or days at a time. The mother lets her get away with anything and my buddy's hands are tied. Is there a way to spy on his daughter's activity without the mother and daughter finding out???? He fears that some maniac will and kill his daughter. I told him i will try to out some info as best as possible!!! I read horror stories how young girls are d and killed. or forced into prostitution and drugs!! please help.....