The central question in this study is how, for whom, and under which conditions professional youth work contributes to the personal development of socially vulnerable youngsters, the reinforcement of their social network, the enhancement of their social participation, and the timely finding of appropriate specialized care services in relation to contextual factors such as life events and the influence of significant others. This research used a multiple case study with a comparative design. During a 12-month period, youth workers (N = 20) participated in group intervision meetings and kept diaries reporting on their actions and the development of the youngsters (N = 23). An analysis of this data revealed four patterns of development of socially vulnerable youngsters in youth work settings. Each pattern consisted of a specific form of multi-methodic action that resulted in a specific outcome. The study also revealed how these processes of development are influenced by important life events and significant others. The findings suggest that youth work contributes to personal development and social participation and thereby may lessen the need for formal social care services.