Three studies were conducted to investigate how social media affordances influence individuals’ source credibility perceptions in risk situations. The MAIN model (Sundar, 2008), warranting theory (Walther & Parks, 2002), and signaling theory (Donath, 1999) served as the theoretical framework to examine the effects of bandwagon cues and identity cues embedded in retweets and users’ profile pages for health and risk online information processing. Study One examines whether bandwagon heuristics triggered by retweets would influence individuals’ source credibility judgments. Study Two investigates how bandwagon heuristics interact with different identity heuristics in credibility heuristics on an individual level. Study Three explores bandwagon heuristics at the organizational level. Three post-test only experiments with self-report online surveys were conducted to investigate the hypothesis and research questions. Results indicate that different online heuristic cues impact the judgments of competence, goodwill, and trustworthiness at different levels. Authority strongly influenced source credibility perceptions. A reverse-bandwagon effect was observed in influencing source credibility judgments. Theoretical and practical implications are discussed.