Teens often encounter cyberbullying on social media. One promising way to reduce cyberbullying is through empowering teens to stand up for their peers and cultivating prosocial norms online. While there is no shortage of bystander interventions that have shown potential, little research has explored designing chatbots with users to provide a contextualized and embedded “learning at the moment” experience for bystanders. This study involved teens and educators in two design sessions: an in-depth interview to identify the barriers that prevent upstanding behaviors, and interaction with the “social media co-pilot'' chatbot prototype to identify design guidelines to empower teens to overcome these barriers. Qualitative analysis on the conversations from the two design sessions revealed three factors that curb teens' upstanding behaviors: a) inadequate knowledge about social norms, appropriate language, and consequences, b) inhibitive emotions such as fear of retaliation and confrontation; c) lack of empathy toward their peers. Key parameters were also identified to shape chatbot responses to encourage upstanding behaviors, such as a) adopting voices representing multiple roles, b) empathetic, friendly and encouraging tone, c) reflective, specific and relatable language and d) appropriate length. These insights inform the design of personalized and scalable education programs and moderation tools to combat cyberbullying.