How can support organisations build the capacity of volunteer-driven non-governmental organisations (NGOs)? Citizen aid for relief and development has expanded rapidly in the twenty-first century, and the number of American aid organisations operating in the Global South has grown to nearly 10,000. These grassroots international NGOs – GINGOs – are small-budget, volunteer-driven organisations typically launched by Americans without professional experience in international development or nonprofit management. These groups prize the expressive and voluntaristic dimensions of development work, yet face challenges of amateurism, material scarcity, fragmentation, paternalism and restricted focus. We investigate whether support organisations, whose primary goals are to build the capacity of organisations and strengthen the organisational field, offer solutions to GINGOs’ inherent weaknesses. We draw on 15 semi-structured interviews with a stratified selection of support organisations, including associations tailored towards international development and towards nonprofit work at large. We find that support organisations offer resources to help GINGOs in managerial and administrative domains. Fewer support organisations help GINGOs build technical development skills, and fewer still push GINGOs to critically reflect on their role in development. We find that peer learning and online platforms could help engage GINGOs volunteers in networking spaces, even as their geographic dispersal in the US encourages their fragmentation and isolation.