We get this in our neighbourhood - they don't do anything really, just make a lot of noise. I guess they're bored.
I have to admit that I used to do the same thing as a teenager - we'd roam around talking (and probably making lots of noise and being obnoxious). It was a small town and there wasn't anything else to do.
Teenagers go out - I'm not sure what you can do except maybe try to raise your kids to be considerate and responsible.
I don't think my parents were negligent or uncaring, but they didn't know where I was a lot of the time when I went out. Must be stressful - I so look forward to having teenagers. not.