The rapid growth of online tourism platforms and increasing competition in this field have made identifying the factors influencing users’ purchase intention a strategic necessity. Among these factors, perceived social presence—one of the key components of user experience in digital environments—can activate motivational mechanisms that lead to purchasing behavior. The present study aims to explain how perceived social presence affects users’ purchase intention on online tourism platforms by examining the mediating roles of utilitarian and hedonic motivations. This research adopts a quantitative approach and is based on survey data collected from 181 users of online tourism platforms, including Jabama, Alibaba, Jajiga, SnappTrip, and Eghamat24 in Iran. The conceptual model was tested using structural equation modeling with the partial least squares approach (PLS-SEM). The results indicate that perceived social presence has a positive and significant effect on purchase intention and simultaneously strengthens both utilitarian and hedonic motivations. However, only utilitarian motivations showed a significant mediating role in the relationship between perceived social presence and purchase intention, while the mediating effect of hedonic motivations was not supported. These findings suggest that in the context of online tourism, functional and rational pathways play a dominant role in transforming digital social interactions into purchase decisions, highlighting the importance of enhancing efficiency, ease of use, and transparency in the design of online tourism platforms.