Social media play an important role in political mobilization. Voluntary engagement can especially benefit from new opportunities for organizing collective action. Although research has explored the use of Twitter by decentralized individuals for this, there has been little emphasis on its use for community engagement and the provision of public goods. Even less is known about its role in the emergence and offline expansion of spontaneous self‐organized solidarity initiatives. This paper investigates how networked communication facilitates self‐organization and the development of ties in a network of volunteers in Greece. To examine whether initiative‐specific community feelings that can transcend online‐offlsine divides evolve in such hybrid networks, the analysis is complemented with individual‐level data drawn from a survey with the initiative's volunteers.