In this paper, we examine how startup support interventions are orchestrated and scaled over time by zooming in on the micro-foundations that underpin their functioning. Specifically, we show how interventions that change existing venturing behaviors emerge from the interplay between macro-level ecosystem characteristics (e.g., structure, governance, and institutions) and micro-level communal initiatives, which themselves are facilitated (or impeded) by strategies to help maximize their reach and propagate their impact. We illustrate this process through an in-depth case study tracing the evolution of a startup-incumbent matchmaking program from a small pilot project to a national flagship initiative in Sweden. We introduce the concept of "ecosystem work” to capture the coordinated efforts to foster a diverse and co-evolving network around the intervention with the ultimately goal of fostering venturing activities. Our micro-foundational model of entrepreneurial support contributes to research by theorizing how localized changes to individual-level (inter)actions can transform venturing behaviors in the ecosystem, thereby illuminating new strategies for intermediaries seeking to foster entrepreneurial activity in more relevant, efficient, and scalable ways.