The shift toward digital advocacy tools has provided advocacy groups with a vital platform to transition their activities online, offering an opportunity to empower historically marginalized demographics, including disabled citizens, ethnic minorities, and women, in political participation. However, emerging evidence points to a potential replication of offline political engagement patterns within online advocacy actions, potentially amplifying the voices of already powerful entities. This raises the question of how digital advocacy can effectively stimulate engagement and bolster the political influence of historically marginalized demographics. To address this question, we designed field experiments in collaboration with advocacy groups aimed at evaluating the impact of integrating content that enhances public efficacy on the political engagement of marginalized communities. These experiments are structured as multistage randomized control trials conducted through Facebook campaigns covering different advocacy issues. We start by testing the impact of efficacy on public engagement with a petition and the use of digital tools to contact political representatives by comparing the effect of different types of campaign content. To shed light on the mechanisms driving these effects, we also investigate individual-level variation in the effectiveness of our treatments leveraging data generated through pre- and post surveys, which are subsequently linked to social media activity of the experiments’ participants.