University sustainability leaders can strategically employ social media tools to encourage the adoption of sustainability behaviors among students, faculty members, and staff. Their effectiveness and reach, however, are constrained by campus sustainability leaders' interpretation of social media. We investigated the perceived functions of social media held by the top sustainable universities in the United States to engage stakeholders in sustainability matters using social media. Interviews with sustainability officers and student leaders at 21 universities revealed that leading U.S. sustainable universities do rely on social media channels to reach large audiences; however, sustainability leaders do not fully understand how to effectively use them. Sustainability leaders primarily perceive social media platforms as useful for encouraging action and disseminating information, but they rarely use it to build community around causes and groups.