Teen.com has a great list of slang taken from MTV's new show Awkward:
Should You Offish Add These New Abbrevs & Slang Words to Your Vocab?
How many of them have you heard used by real live teens? What new slang have you heard recently your peers might want to know about?
I would seriously hesitate before deliberately incorporating any of these in conversations with teens if you are trying to look cool...because that stuff always backfires! But knowing what they are saying is a good advantage to have, both so you can be understanding, and have a bit more of a clue as to what really is going on around you ;)
Other teen slang sources: