Examining the sources of health communication that young adults with mental health challenges receive regarding service use is critical to curbing the societal concern of unmet mental health needs of this population. Semistructured interviews were conducted with 59 young adults, all of whom were diagnosed with a mood disorder and used public mental health services and additional public systems of care during childhood. Thematic analysis was utilized. Of the 59 participants, 45 nominated at least one supportive adult, with a total of 97 relationships analyzed. Results indicate that the majority of messages came from informal supports (e.g., family) who spoke positively about mental health services. Fewer messages came from formal supports (e.g., professionals). Messages included statements surrounding beliefs toward services, social norms (approval and disapproval), self-efficacy, and image considerations around using services. These findings can suggest ways that mental health service engagement interventions can leverage communication from informal supports. Future research can explore what messages young adults find most influential in persuading them to use mental health care consistently and the relationship between messages and health behavior.