Sustainability plans are essential for fostering prosperous cities for present and future generations. The degree of citizen agency, control, and power in shaping plans varies across different participatory mechanisms. Despite its popularity and ubiquity, how social media, as a new form of participatory mechanism, shapes government sustainability plans remains relatively unclear. Therefore, by using a 2015 nationwide survey of U.S. local government administrators, this study examines social media’s influences on plan adoption and design, particularly in comparison to conventional participatory mechanisms. The findings provide insights for public managers on how to leverage different participatory mechanisms in advancing a sustainability plan.