Background: AYAs diagnosed with cancer report psychological challenges and social isolation due to their situation. Peer support has been shown to be a valuable resource for coping with these experiences. Aim: The aim of this study is to map the needs for emotional peer support among AYA cancer patients in Sweden; and building on these results to develop and test a prototype of a digital tool for peer support between AYA cancer patients. Method: The study was conducted in close collaboration in a research team consisting of AYA cancer survivors, researchers, and a health tech company in Sweden. Through interviews the needs for emotional support among was investigated. Based on this information, a prototype of a digital platform was co-created by the research team. The platform was tested by AYAs and evaluated through an online survey and follow-up interviews as part of the iterative development process. Results: The AYAs described feeling lonely and having a need for processing their cancer experiences with peers. A combination of support through interaction with peers in both digital and physical meetings was preferred. A prerequisite for being a valuable resource, the digital platform had to have a high degree of security. Piloting the prototype, 87% reported feeling secure, all participants found it valuable to interact with peers on the platform. In the follow-up interviews the AYAs reported the log-in procedure to be difficult and the need to make this easier, while still maintaining high security. Conclusion: A secure digital platform for peer support can be a valuable and easily accessible a complement to other forms of support. The presence of moderators was found to enhance security and perceived usefulness of the platform. Co-creating tools for support with AYAs ensures relevance and usability. Acknowledgement: We thank all AYA cancer patients for participating in this study.