Am I irresponsible for letting this happen?

I was palying this game on facebook with my friends and some random guy made his way through the game. I have my picture on facebook and the guy kep saying he wanted me and he wanted to talk to me on aim. I was so scared because he looked about 50 and kept making me uncomfortable. i tried to block him but it wouldn't work. I'm 15 years old. What should i do?