Ask-Boost-Connect-Discuss (ABCD) is a mobile-based tool to improve maternal mental health among adolescent mothers living with HIV, delivered by peer supporters in low-resource settings. Peer supporters are young people living with HIV who are engaged in existing networks with health services. The original package of care for ABCD proposed included: screening psychosocial needs of young mothers (“Ask”), mental health support (“Boost”), help with accessing services (“Connect”), and ongoing supervision and self-care (“Discuss”). The original ABCD app (an ABCD prototype) was designed through an ongoing co-development process with end-users and carried out in four focus countries (Uganda, Tanzania, Malawi, and Zambia). Across all sites, attendance in ABCD-related group activities was high and the pilot programme was found to be feasible, acceptable, valuable, and responsive to the needs of both peer supporters and the young moms they supported. These practical findings indicate that a technologically-based tool can equip peer supporters to provide psychosocial support to adolescent mothers.