In this paper, we examine when members of underrepresented groups choose to support each other, using the context of the funding of female founders via donation-based crowdfunding. Building on theories of choice homophily, we develop the concept of activist choice homophily, in which the basis of attraction between two individuals is not merely similarity between them, but rather perceptions of shared structural barriers stemming from a common social identity based on group membership. We differentiate activist choice homophily from homophily based on the similarity between individuals ("individual choice homophily"), as well as from "induced homophily," which reflects the likelihood that those in a particular social category will affiliate and form networks. Using lab experiments and field data, we show that activist choice homophily provides an explanation for why women are more likely to succeed at crowdfunding than men and why women are most successful in industries in which they are least represented.