Blackmailed with nude pics of me. Help!!!?

Ok so i was stupid and sent a total stranger nude pics of me and now he is blackmailing me. I think he has made numerous email accounts. I am 15 and dont know how old he is. i think there is also more than one guy involved. I need help he is now blackmailing me making me cam on msn and send them more pics of me. Do i let the world see, keep going, or tell the police. Or any other advice thank you.