The present study examined the impact of socially based descriptive norms on willingness to drink alcohol, drinker prototype favorability, affective alcohol attitudes, and perceived vulnerability for alcohol-related consequences within the Prototype Willingness model. Descriptive norms were manipulated by having 189 young adolescents view experimenter-created profile pages from the social networking site Facebook, which either showed older peers drinking or not. The results provided evidence that descriptive norms for alcohol use, as portrayed by Facebook profiles, significantly impact willingness to use, prototypes, attitudes toward use, and perceived vulnerability. A multiple mediation analysis indicated that prototypes, attitudes, and perceptions of use mediated the relationship between the content of the Facebook profile and willingness. These results indicate that adolescents who perceive that alcohol use is normative, as evidenced by Facebook profiles, are at higher risk for cognitions shown to predict alcohol use than adolescents who do not see alcohol use portrayed as frequently on Facebook.