I don't know anyone with a twitter account. When I was a teenager (2 years ago heh) all I used was msn/irc. Facebook/gmail chat seems to be a bit more popular among the kiddes these days though.
Geography plays a strong role as well. In the US AIM is super popular (until it was supplanted by gchat in my clique). European friends used to use ICQ (long ago), and I think MSN has been generally popular in Asia forever.