JUUL is the most popular electronic nicotine delivery system (ENDS) in the United States. JUUL’s discreet design, availability in flavors such as mango, and use of nicotine salt solutions that deliver a high dose of nicotine with minimal harshness may explain its appeal. Nearly 64.2% of high school students have ever used JUUL, and 47.1% currently use JUUL. Social media may have fueled JUUL’s popularity. The number of Tweets about JUUL rose dramatically in 2015 to 2017, corresponding with the sharp increase in JUUL retail sales. Online conversations about JUUL were rarely about quitting smoking and more commonly about pods, purchasing, and use (eg, “juuling” in school). JUUL’s online advertising strategy was youth focused; they used young adult models, marketed sweet and fruity flavors, and used social media influencers to promote the brand. Youth exposure to ENDS advertising increases susceptibility to and trial of ENDS among potential new users. To date, and to our knowledge, no study has examined whether youth and young adults are exposed to JUUL marketing on social media. This study used a previously developed computational age-prediction algorithm to determine the extent to which underage youth are following the JUUL brand account on Twitter.