I know my kids hated me in their teen years because I had a rule that I enforced. IF they were going to be on line I was to have all their passwords to any site they went on. I also did random checks on their computers to see where they were going and what they were doing on the computer. Failure to comply was loss of electronics. This included cell phone, ipods, game station, lap tops/desk tops. If they cleared search histories same thing for a week. I wanted to make sure they were acting correctly and not getting themselves in any trouble.
I have sen what some kids post on line and I say it is disturbing in some cases. I think there area lot of parents out there that have no real clue to what their kids are doing.
Teens don't have much control and their curiosity is at a very high level. They are able to get away with a lot because of the internet because it satisfies that curiosity in an unrestricted way. You just have to monitor what they're doing.