While cyberbullying is prevalent among adolescents, attempts by researchers to evaluate mechanisms for its prevention and mitigation have been largely non-existent. In this dissertation, I argue that the complex nature of cyberbullying, made more challenging by the affordances of diverse social media, cannot be solved through strictly algorithmic approaches. Instead, I employ multidisciplinary methods to evaluate data generated by teens on social media and work with teens to develop and test potential cyberbullying mitigation solutions. I further argue that solutions focused on improving users' well-being after being targeted online offer designers a valuable tool in fighting back against the harm caused by cyberbullying. Based on the interdisciplinary studies conducted in this dissertation, I offer design recommendations for cyberbullying prevention and mitigation tools.

I address the mitigation of adolescent cyberbullying through a multi-methodological approach: 1) data-centric exploratory study of discourse occurring alongside cyberbullying 2) an experimental design of reactions to positive messages in response to cyberbullying 3) human-centered participatory design to design cyberbullying mitigation prototypes and 4) a longitudinal study evaluating the effectiveness of cyberbullying mitigation tools. I offer design recommendations for building and administering cyberbullying mitigation tools. This dissertation begins with a data-centric study to understand \textit{why} users are motivated to post and interact through ASKfm, a social media platform that affords cyberbullying and how anonymity and the site's other affordances affect these interactions. I discuss the unique affordances specific to semi-anonymous Q&A social media platforms and how such affordances enable users to engage in self-disclosure and gaining social support on sensitive topics. I then present two studies to first determine if users will be receptive to anonymous positive messages responding to bullying messages, then to administer positive messages or \textit{Cyberbully Reversal Pings} to ASKfm users who have received bullying messages. I then use a human-centered approach methodology to co-design cyberbullying prototypes with teens.

I use the design recommendations derived from the participatory design study to test the impact of a cyberbullying mitigation system. I address technological mechanisms to mitigate sadness and decline in well-being caused by negative online experiences and cyberbullying. I administer cyberbullying mitigation through technology-mediated memory; in other words, I use positive posts and images participants have previously shared on social media to remind them of existing social support in users’ social networks. The studies in this dissertation comprise of a mixed methods approach to understand social media platforms on which cyberbullying occurs, work collaboratively with users to design mitigation platforms and ultimately evaluate a cyberbullying mitigation platform with real users. These aforementioned studies result in design recommendations for building cyberbullying mitigation tools and design recommendations for designing a study to evaluate a cyberbullying mitigation tool.