It depends,its positive if they use it for the right reasons.For instance,the internet.They use Facebook all day(or just about)and let their school work decline,to some friends are more important,I'm sure some are in school on their phones texting as you read this.Of course that would be the negative side. Even the advancement of game technology draws them away from schooling.You see some of those awesome graphics! I get hooked sometimes.Of course the parents NEED to play a role in it to correct the situation,which doesn't happen much.
Personally, technology has more of negatives than positives on teens. It exposes them to too much which can be harmful in various ways. There are those who can use the technology for bad things like hacking websites or even going to adult rated websites. The technology is good in terms of the education, but the bad out ways the good in this.