There is a scary movie from the 90s I think that talks about a boy who meet a homeless girl and help her to escape from a man who want to kill her, and in the way he kill her homeless friends group. The movie has a sex sciene in it (just another clue).
Please I need your help I looked for it for time because it's the most amazing scary movie ever.

Any chance it's this?
STREETS - 1990 Trailer - YouTube (http://www.youtube.com/watch?v=V4AXt_NV6Yw)