Engaging youth in civic participation is essential for sustainable societies. Social robots, as embodied and interactive entities, may be feasible tools to spark youth’s interest. To start designing persuasive interactions for this purpose, we conducted a study addressing the question, what do youth consider as appropriate behaviour for a civic robot? We developed three scenarios describing social robots as persuaders for youth’s civic participation. The scenarios were evaluated in three workshops with 51 fifteen-year-old Finnish participants. The credibility of the robot emerged as a central theme: a civic robot should emphasize its purpose and avoid any pretence—also when expressing emotions.