Food-related promotion of brands via social media represents an increasingly important youth-targeted marketing strategy, but little is known about how adolescents interact with these brands online. This study measures adolescents’ social media engagement with food/beverage brands, sociodemographic differences in level of engagement, and relationships between engagement and screen time. Cross-sectional online survey of US adolescents (ages 13–17, N = 1564), oversampled for non-Hispanic Black and Hispanic (more- and less-acculturated) participants, assessed restaurant, food, and beverage brands ever liked, shared, or followed of on social media. Multivariate logistic regression models examined associations between brand engagement, sociodemographic variables (race/ethnicity, acculturation, age, gender, and parent education), and screen time (TV and other screens). Seventy percent of adolescents reported engaging with any food/beverage brands on social media (ranging from 1 to 48), and 35% engaged with 5 + brands. Non-Hispanic Black and less-acculturated Hispanic adolescents were more likely than non-Hispanic White adolescents to engage with brands. Approximately one-half reported engaging with brands of fast food (54% of participants), sugary drinks (50%), candy (46%), and snacks (45%), while just 7% reported engaging with all other categories of food/beverage brands. Watching TV more than 2 h-per-day was associated with any brand engagement; while using other screens more than 2 h-per-day was associated with following 5 + brands. Engagement with unhealthy food brands on social media is common among adolescents. Disproportionate engagement by non-Hispanic Black and less-acculturated Hispanic youth raises additional concerns. Research is needed to understand how such marketing affects adolescents’ food preferences, diets, and health.