This study explores transnational diffusion of social movement information in social media by introducing a mathematical model. Although the literature extensively discusses social media uses in social movements, few studies have examined a spatiotemporal dynamic diffusion process. Even fewer have taken into account international relational factors that may interplay with the diffusion process. This study addresses this gap by examining different notions of spatial proximity—each of which pertains to the level of democracy, diaspora size, economic relations, and physical distance—and applying them to a mathematical “diffusion-advection” model. The model was validated by tweets during the Egyptian revolution of 2011. The spatial diffusion was most effectively explained when the model was fitted using a democracy-based spatial arrangement. Although the diffusion of ad hoc reporting and action supportive messages were particularly in high volume during the most active protest period, situation-verifying information was diffused at a steady pace throughout the entire period examined. By demonstrating the model’s validity with the Egyptian revolution Twitter data, the article reveals the potential of using mathematical modeling in social movement research.