“Cadê o Kauê?” is an interactive digital story that takes place in an instant messaging platform. The user’s quest is to find their best friend, Kauê, who has gone missing on the day of the opening night of a school play. As the narrative unfolds, it becomes clear that Kauê has been facing mental health difficulties, and the user has the opportunity to help him and others at school. Co-designed by an interdisciplinary team of researchers, young people and narrative designers, “Cadê o Kauê?” aims to strengthen Brazilian young people’s ability to promote their peers’ mental health, via peer support and collective action. design process and methods; Participatory design; Human computer interaction (HCI); Interactive systems and tools.