Background Tailored, web-assisted interventions can reach many smokers. Content from other smokers (peers) through crowdsourcing could enhance relevance. Purpose To evaluate whether peers can generate tailored messages encouraging other smokers to use a web-assisted tobacco intervention (Decide2Quit.org). Methods Phase 1: In 2009, smokers wrote messages in response to scenarios for peer advice. These smoker-to-smoker (S2S) messages were coded to identify themes. Phase 2: resulting S2S messages, and comparison expert messages, were then e-mailed to newly registered smokers. In 2012, subsequent Decide2Quit.org visits following S2S or expert-written e-mails were compared. Results Phase 1: a total of 39 smokers produced 2886 messages (message themes: attitudes and expectations, improvements in quality of life, seeking help, and behavioral strategies). For not-ready-to-quit scenarios, S2S messages focused more on expectations around a quit attempt and how quitting would change an individual's quality of life. In contrast, for ready-to-quit scenarios, S2S messages focused on behavioral strategies for quitting. Phase 2: In multivariable analysis, S2S messages were more likely to generate a return visit (OR=2.03, 95% CI=1.74, 2.35), compared to expert messages. A significant effect modification of this association was found, by time-from-registration and message codes (both interaction terms p<0.01). In stratified analyses, S2S codes that were related more to "social" and "real-life" aspects of smoking were driving the main association of S2S and increased return visits. Conclusions S2S peer messages that increased longitudinal engagement in a web-assisted tobacco intervention were successfully collected and delivered. S2S messages expanded beyond the biomedical model to enhance relevance of messages. Trial registration This study is registered at www.clinicaltrials.gov NCT00797628 (web-delivered provider intervention for tobacco control [QUIT-PRIMO]) and NCT01108432 (DPBRN Hygienists Internet Quality Improvement in Tobacco Cessation [HiQuit]). © 2013 American Journal of Preventive Medicine.