Moral outrage predicts the virality of petitions for change on social media, but not the number of signatures they receive

Social media platforms help activists to share their perspectives. However, there is concern that amplified content (e.g., moral outrage) may limit collective action. We studied how online petitions on www.change.org were shared and signed. Analyzing posts on X (n = 1,286,442) with URLs to petitions (n = 24,785) revealed that expressions of moral outrage were uniquely associated with the number of times posts were liked and reposted (virality). Mediation analyses showed that outrage was indirectly related to the number of signatures petitions received (via virality). However, outrage was associated with fewer signatures when controlling for virality. In contrast, expressions of agency, group identity, and prosociality were associated with more signatures but no more virality. The findings outline the factors linked to engagement with online petitions and describe how social media can amplify content which has no direct link to the sorts of effortful behaviours which are conducive to social change.