I'm not really sure they'll work, but they're worth signing, as they take what? 5 seconds to sign?
http://tvseriesfinale.com/tv-show/heroes-petition-to-continue-the-nbc-tv-show/
http://www.petitionspot.com/petitions/saveheroes/donate
http://tvseriesfinale.com/tv-show/heroes-petition-to-continue-the-nbc-tv-show/
http://www.petitionspot.com/petitions/saveheroes/donate