This study examines direct and indirect effects of interactive communication in an antismoking social media campaign. To that end, we pose a multitheoretical framework that integrates communication mediation models and the Theory of Planned Behavior. To test the theorized model, we conducted an experiment using a two-group pretest-posttest design. Participants (N = 201) were randomly assigned into two experimental conditions: "campaign message reception only" as a control group and "message reception and social interaction" as a treatment group, in which the participants contributed to the antismoking campaign by posting their own campaign ideas and information they found through mediated and interpersonal communication. The findings show that interactive communication catalyzes the participants' information searching behaviors through diverse communication channels. In turn, increased media use plays a crucial role in changing their attitudes and perceived social norms about smoking behaviors, and eventually reducing smoking intention. This study affirms that the theory of planned behavior is effective in predicting behavioral intention and demonstrates the usefulness of a multitheoretical approach in interactive campaign research on social media.