Background: Alcohol and binge drinking pose significant health risks, especially for underage women; nonetheless, binge drinking is common. Materials and Methods: To evaluate the effectiveness of the PartyWise intervention in increasing awareness of sex differences in the risks of binge drinking, we used social media to enroll 520 female adolescents aged 15-19 years in a randomized controlled trial. Intervention participants received telephone screening, a brief counseling intervention with web-based resources (http://www.partywise.org), and up to 8 weekly text messages. Results: At baseline, most (71%) participants reported alcohol consumption in the prior month and 44% reported binge drinking (four or more drinks on one occasion), without differences between study groups; 79% of participants were aware of sex-based differences in alcohol risks. At follow-up, intervention recipients were more knowledgeable about sex-based differences in alcohol risks (adjusted odds ratio [adj OR] 8.87, 95% confidence interval [CI] 3.35-23.49 at 3 months; adj OR 2.44, 95% CI 1.21-4.90 at 9 months) and more likely to accurately define binge drinking (adj OR 1.63, 95% CI 1.02-2.60 at 3 months; OR 1.37, 95% CI 0.89-2.06 at 9 months). Although rates of any binge drinking in the past month remained similar between groups, intervention recipients were less likely to report binge drinking more than once in the past 30 days (22% vs. 32%, adj OR 0.58, 95% CI 0.35-0.99 at 3 months; 27% vs. 30%, adj OR 0.97, 95% CI 0.60-1.55 at 9 months). Conclusions: The PartyWise intervention is a promising approach to increasing awareness of the risks of binge drinking for underage women in a remotely delivered platform. Clinical Trials Registration: The Share Health Study: Teen Social Connections and Health (Phase 2), NCT03842540, https://clinicaltrials.gov/ct2/show/NCT03842540?id=NCT03842540&draw=2&rank=1.