Tobacco use and heavy episodic drinking (HED) commonly co-occur in young adults. We developed and tested usability of the Smoking Tobacco and Drinking (STAND) intervention for young adults delivered on Facebook. To inform the intervention, focus groups were held with 25 young adults age 18 to 25 (12% female; Mean age = 20.4) who smoked cigarettes and reported at least one HED episode in the past month. Facebook intervention posts (N = 180) were tailored to readiness to quit smoking, and tested in two private Facebook behavioral change groups (Ready, Not Ready) with N = 29 young adults (10% female; Mean age = 20.8). Participants flagged posts in need of change, and we assessed engagement (comment frequency). Focus groups revealed preference for changing one substance at a time and greater receptivity to quitting smoking than reducing drinking. Mean comments per post were 5.3 (SD = 1.1) in Ready groups and 11.7 (SD = 5.1) in Not Ready groups; 94/180 (52.2%) posts were flagged for change. The level of engagement and the flagging of posts for change did not differ by group or by whether the post targeted tobacco, alcohol, or both substances combined (all p > .10). Overall, STAND was rated as easy to understand, providing sound advice, worthy of recommendation, and helpful (all agreement 100% among Ready; 50-70% among Not Ready). The current findings informed development of a social media-based intervention targeting tobacco and alcohol use in young adults. Although there was greater interest in making changes in smoking than drinking behavior, receptivity and acceptability of the Facebook post messages in the STAND intervention was high overall. The intervention is being further refined for evaluation in a larger trial. Trial registration Name of the registry Smoking Tobacco and Drinking Study (STAND); Trial registration number NCT03163303; Date of registration 5/23/17; URL of trial registry record https://clinicaltrials.gov/ct2/show/NCT03163303 .