If I was a real bastard, I'd surreptitiously promote something like one of those JBG/skittles type site heheh
But seriously, this is going to make you look like the biggest pedo when you get to the counter, but go to the newsagent/magazine store and get yourself the latest issues of Cleo, Dolly, Teenscene, whatever the fuck magazine in your area is aimed at girls in that age group.
Don't just look at the ads (although those are the obvious things to go for). Most of the articles in those mags are actually paid for advertorials where the "writers" shill themselves out to whatever company they're sucking off that month. The shit they're pushing in those articles will be what's hot next month with all the little sheeple.
...and the exact opposite will be what's hot with all the inDUHviduals (like emos).