In general I think the homeless don't want to cause trouble. As long as they don't cause problems the police won't run them off. However, gangs and young wannabes will cause problems as that what they're out there to do. Unfortunately, most youths hanging out at night who don't want trouble look the same as those looking to cause trouble.
I live in Washington county and frequently use the multiuse path between Tigard and Beaverton at all hours of the day. So far, I've rarely seen anyone who looks like trouble. But this weekend the path between Denny and Hall was vandalized with a streetlight knocked down to block the path, an well as a lot of lumber (probably the remains of someones fence) scattered in such a way as to block the path. I'm sure those individuals would have been scary to encounter especially as that portion of the path has no easy escape paths, a lot like the Springwater trail. So the problem is everywhere, it's just worse in some places.