The influence that marketing for foods high in fat, salt, and/or sugar (HFSS) has on adolescents extends beyond a dose-response relationship between exposure and consumption. It is also important to explore how marketing shapes or reinforces product/brand attitudes, and whether this varies by demography and Body Mass Index (BMI). To examine this, a cross-sectional survey was conducted with 11–19 year olds in the United Kingdom (n = 3348). Participants watched 30 s video adverts for a fast-food and confectionery brand. For each advert, participants reported reactions on eight measures (e.g., 1 = Makes [product] seem unpopular choice–5 = Makes [product] seem popular choice), which were binary coded based on whether a positive reaction was reported (Yes/No). At least half of adolescents had positive reactions to both adverts for 5/8 measures. Positive reactions had associations with age, gender and, to a lesser extent, BMI. For example, 11–15 year olds were more likely than 16–19 year olds to report appeal to their age group for the fast-food (OR = 1.33, 95% CI: 1.13–1.58) and confectionery advert (OR = 1.79, 95% CI: 1.52–2.12). If these reactions are typical of other HFSS products, future research and regulatory change should examine whether additional controls on the content of HFSS marketing, for example mandated health or nutritional information and revised definitions of youth appeal, offer additional protection to young people.