Objective: To estimate the causal effects of online community use on 30-day point prevalence abstinence at 3 months among smokers that received a combined Internet/phone intervention for smoking cessation. Method: Participants were 399 adult smokers selected from the combined Internet/phone arm of The iQUITT Study (Graham et al., 2011), a randomized trial of Internet and proactive telephone counseling for smoking cessation. All selected participants had accessed a web-based smoking-cessation program with an established online community and received at least one telephone counseling call. Automated tracking metrics of passive (e.g., reading posts, viewing profiles) and active (e.g., writing posts, sending messages) community use were extracted at 3 months. Self-selected community use defined the groups of interest as None, Passive, and Both (passive and active). Inverse probability of treatment weighting corrected for baseline imbalances on demographic, smoking, and psychosocial variables. Propensity weights estimated via generalized boosted models were used to calculate average treatment effects (ATE) and average treatment effects on the treated (ATT). Results: Patterns of community use were None = 145 (36.3%), Passive = 82 (20.6%), and Both = 172 (43.1%). ATE-weighted abstinence rates were None = 12.2% (95% CI = 6.7–17.7), Passive = 25.2% (95% CI = 15.1–35.2), and Both = 35.5% (95% CI = 28.1–42.9). ATT-weighted abstinence rates indicated even greater benefits of passive community use by nonusers. Conclusions: More than 1/3 of the participants who used the community both passively and actively achieved abstinence. Participation in an established online community as part of a combined Internet/phone intervention has the potential to promote short-term abstinence. Results also demonstrated that information and support that originate in the community can serve as a resource for all users.