As Internet-based tactics become commonplace in public relations practice, targeting campaigns to specific publics becomes more challenging. The global reach of the Internet challenges a public relations practitioner’s confidence that an online message targeted at a set of specific demographics will reach only the intended audience. Internet-based public relations campaigns can attract unexpected, or even unwanted, publics to a project or brand, and practitioners must be ready to manage these unexpected participants. This article examines unexpected publics that engaged an online public participation project focused on architectural design and transit planning. The project, which was targeted at everyday bus riders in Salt Lake City, Utah, attracted an international base of design professionals. These unexpected publics, who learned of the project through the Internet, caused global-local and amateur-professional tensions that complicated the outcomes of the project. Through website analytic data, user registration data on the website, and interviews with project participants, this article explores these tensions and offers practical advice for managing unexpected publics online.