This study examines how influencer marketing compares to traditional advertising―online and TV adsin driving sales, both directly and indirectly through electronic word of mouth (eWOM). Using a multi-equation model and real-world data from a global cosmetics company, we estimate channel-specific sales elasticities and returns on marketing investment. Our results show that influencer marketing generates significantly larger sales effects than online and TV advertising, with higher elasticities and greater long-term ROI. Importantly, influencer marketing stimulates eWOM, which mediates additional online sales, revealing an indirect pathway that is less pronounced for conventional advertising. Effects are particularly strong within the online channel, reflecting a channel-matching advantage and the digital nature of social amplification. This study contributes to literature by quantifying both direct and indirect effects of influencer marketing across channels, situating them relative to traditional advertising, and clarifying the role of eWOM as a mediating mechanism. Managerially, the findings underscore influencer marketing as a high-return strategy that drives immediate sales and consumer-driven amplification, offering actionable insights for omnichannel marketing in digital and offline contexts.