A successful Entrepreneurial Ecosystem (EE) depends on productive regional social capital. Social capital is productive if its structural, relational and cognitive dimensions work together (Nahapiet & Ghoshal 1998). In EEs, these dimensions of social capital are ex- pressed through culture, leadership and social networks (Theodoraki et al. 2018, Stam & van de Ven 2021). In order to understand how social capital can help to foster entrepreneur- ship in specific regions, we propose one empirical study design. We employ a Randomized Messaging Experiment (RME) with approximately 58,000 subjects to assess entrepreneurs’ willingness and sources for motivation to support start-up ecosystems. Our hypotheses are that entrepreneurs are more willing to support their own EE; that this willingness varies with EE; and that being part of a common industry is not a defining factor for the entrepreneurs’ support. The studies aim to contribute to the literature by providing an additional quantitative measure of the quality of an EE and by identifying additional levers for policy to increase start-up activity and economic growth.