This study aims to explore the effect of social media use on fundraising by nonprofit organizations (NPOs). To do so, we analyze the accounts of 83 Spanish nongovernmental development organizations on Facebook, Twitter, YouTube, and Instagram over a 5-week period. Our results show that social media can be a useful tool for NPO fundraising. Specifically, although mere presence on social media has no effect on the donations raised by the organization, the size of the NPO’s network (followers), its social media activity (posts), content (posts explicitly requesting donations), and follower engagement do influence fundraising. This study helps to highlight the usefulness of social media as a fundraising tool and to show the differences among platforms, format, and content of posts. In particular, NPOs who intend to increase fundraising should actively participate in social media—especially Twitter and YouTube—not overuse stories and increase posts that solicit donations.