Teenagers are fond of online social networks (OSNs) but may be unable to decipher the marketing messages aimed at them or protect themselves from harmful advertisements, raising ethical concerns. The findings of this study may help alleviate such ethical concerns. Teenagers’ use of OSNs contributes to the development of a social skill—theory of mind (ToM)—which helps them interpret advertisements and detect deceptive contents. With regard to ethics-oriented outcomes, the findings confirm that ToM discourages youth materialism, which may be encouraged by inappropriate advertising, thereby demonstrating the utility of ToM in mitigating the adverse consequences of unethical marketing. Moreover, OSNs have reshaped how teenagers acquire ToM, such that they replace offline interactions (i.e., offline friendship quantity/quality) to play a central role in ToM development. Although OSNs expose teenagers to the harms of online marketing, they also empower teens to enhance their social skills, which potentially protect them from deceptive advertising.