The primary aims tests Hypothesis 1: Relative to usual care (n=240), Tweet2Quit-coed groups (n=480) will achieve significantly greater bioconfirmed sustained abstinence out to 6-months follow-up, and Hypothesis 2: Women in Tweet2Quit will achieve significantly greater bioconfirmed 6-months abstinence in woman-only groups (n=240) vs. coed groups (n=240 women).