Government social media accounts (GSMAs) are increasingly used by government agencies for crisis management. The success of crisis management through GSMAs highly depends on citizens’ participation by commenting on and sharing posts. Drawing on the Civic Voluntarism Model (CVM), this study proposes a research model to explore the key antecedents of citizens’ commenting and sharing behaviors during crises. Through a field survey conducted after the 2015 Tianjin explosions in China, this study demonstrates that emotional support, external political efficacy, rumor control, civic skills, and mobilization are significant antecedents of commenting and sharing, whereas perceived reciprocity only matters for sharing. Moreover, the perceived connectivity of GSMAs moderates several of those relationships. The theoretical contributions and practical implications are discussed.