This study empirically examines how consumers’ search behavior and search advertising effectiveness differ across platform types, namely search engines and commerce platforms. Prior research has largely focused on keyword attributes or ad position as determinants of performance, whereas this study, drawing on the consumer decision journey perspective, examines how platform context shapes keyword type and specificity. The results show that brand-oriented keywords are more prevalent on search engines, while category-oriented keywords are more common on commerce platforms. In addition, commerce platforms generate higher click-through and conversion rates than search engines, but also incur higher cost per acquisition, suggesting a trade-off between performance and cost efficiency. Finally, the effect of keyword specificity differs by platform. On commerce platforms, more specific keywords are associated with higher click-through and conversion rates, whereas on search engines, these differences are not statistically significant. Overall, the findings suggest that search advertising effectiveness depends not only on keyword characteristics but also on the platform environment in which search occurs.