What to do when people dont leave you alone?

Well what happend was on Facebook someone made a profile called peter file and pretended to be a pedophile and was going round slagging people off and saying crap and causing arguments, for days everyone thought it was this girl called kirsty and I said 1ce just 1ce its probley someone from their group ...and now she is spreading round the whole school its me everyone thinks its me now when I walk past people they call me pedo and stuff ... it not even me even some of my ' friends ' don't no who to believe me or them I even ran out of school today because they all ganged up on me :( I am in year 9 I have 2 years left of school how do I cope with all this ... I have my boyfriend and like 3 friends by my side but their not in my lessons to defend me or help me stay strong what should I do :( :( I went to a teacher and they didnt do anything now everyone calls me a snitch aswell ...