You don't get to go around throwing fire and burning bridges... and then expect people to still like and respect you. That's not how it works. If you are nasty and hateful to people, you can't really play the victim or feel sorry for yourself when no one wants to pursue a friendship with you, or even talk to you anymore.
If you have sincerely had a change of heart... ball up and apologize to people. Don't send someone else ("tell everyone I'm sorry") or expect social networking sites to do the job for you ("I sent him a message on facebook..."). That kind of response still lacks maturity and responsibility in every way. And quite honestly, pisses people off.
It is, unfortunately, a long, frustrating, and humbling process to rebuild that bridge you burnt absolutely to the ground, so if you know yourself to be impulsive, immature, fickle, or you opinion easily swayed... next time, I would think very carefully before you get out your flame thrower.