Family members of Veterans with posttraumatic stress disorder (PTSD) face high levels of burden that are poorly addressed by existing mental health services. Widely distributed mobile interventions could play a role in addressing these unmet needs. The purpose of this study was to characterize caregiver burden in those seeking a mobile app for self-management of stress symptoms and to develop a model to guide mobile interventions for family members. Those living with a Veteran with PTSD (n = 212) and interested in using a mobile intervention agreed to participate. The majority reported moderate-to-severe levels of depression (60%) and/or caregiver burden (59%). Relationship quality, communication, and self-efficacy for caregiving were the strongest predictors of negative outcomes (p’s <.001), and qualitative results identified several additional unmet needs (e.g. relationship concerns, safety concerns). This study identifies potential mechanisms by which a mobile app could improve family functioning in the context of PTSD.