This study examined the effect of social media engagement on collective action intention to help Ukrainian refugees. This study proposes a dynamic, transactional model that draws upon computer-mediated communication research and the dynamic dual pathway model of collective action (DPPM) to investigate the impact of two types of social media engagement, namely actions and cues, on intergroup helping. The model aims to achieve two objectives: First, it examines the mediating role of anger and collective efficacy, the two parallel psychological mechanisms proposed by DPPM, in the effects of action and cues on collective action intention. Second, it tests the dynamic and reciprocal relationship between collection action intention and social media actions and cues over time. A three-wave longitudinal survey of U.S. adults was conducted after the Russian-Ukrainian War started. Longitudinal mediation analyses showed that social media action predicted greater collective action intentions indirectly through collective efficacy but not anger. Social media cues did not predict collective action intentions through collective efficacy or anger. Collective action intentions, in turn, increased subsequent social media actions and cues, forming a positive feedback loop. The effect of social media actions on collective action intention was stronger than that of social media cues.