My daughter is not a teen yet but she is into her computer and has her own gmail account and chats on it. I like gmail because it's invite only so you can screen who you can talk to.
My one question/thought that no one's brought up is that it seems like as important (if not more important) than monitoring is talking to your kids about how to keep themselves safe in all situations (chat rooms/cyberspace, meeting strangers, at school, gym, etc) and explaining the notion that while many networking aspects of the internet can seem like an online version of real life groups of friends (eg., Facebook) that they are actually very public with real consequences and teaching/discussing parameters for how to safely and comfortably use them effectively.
In my view, constant monitoring/controlling is not effective because kids are clever and always find ways to rebel. If they haven't been taught how to take care of themselves and how to trust and come to you with things then they can get hurt regardless of the level of monitoring. I would rather focus on building a trusting relationship and creating forums for open and honest discussion. I think you can pay really close attention without constantly supervising. I think this method would go triple time for a stepkid you're just developing a relationship with.
Also, fwiw, on the hickey: I think kids at this age are just beginning a whole process of sexual exploration and it's totally normal and developmentally appropriate. Again, I think the key is trust and open communication to help kids learn how to explore and deal with their increasingly powerful and frequently overwhelming new feelings.