Young carers provide a substantial amount of care to family members and support to friends, yet their situation has not been actively addressed in research and policy in many European countries or indeed globally. Awareness of their situation by professionals and among children and young carers themselves remains low overall. Thus, young carers remain a largely hidden group within society. This study reports and analyses the recruitment process in a multi-centre intervention study offering psychosocial support to adolescent young carers (AYCs) aged 15–17 years. A cluster-randomised controlled trial was designed, with recruitment taking place in Italy, the Netherlands, Slovenia, Sweden, Switzerland and the United Kingdom exploiting various channels, including partnerships with schools, health and social services and carers organisations. In total, 478 AYCs were recruited and, after screening failures, withdrawals and initial dropouts, 217 were enrolled and started the intervention. Challenges encountered in reaching, recruiting and retaining AYCs included low levels of awareness among AYCs, a low willingness to participate in study activities, uncertainty about the prevalence of AYCs, a limited school capacity to support the recruitment; COVID-19 spreading in 2020–2021 and related restrictions. Based on this experience, recommendations are put forward for how to better engage AYCs in research.