This dissertation aimed to shed light on the role of the social network in supporting urban at-risk youths. The findings presented highlight the importance of recognizing that at-risk youths’ social sources may not always adequately meet their needs, possibly because the bonding social networks are under some of the same stressors as youth themselves. Findings suggested that this lower social support is often associated, or has consequences for, youths’ wellbeing. The studies also demonstrated the importance of adjusting support to the needs of these youths’ and to provide them with additional instrumental and informational support from bridging social networks. This additional support may come from supportive non-parental adults in mentoring programs. The findings in this dissertation provide empirical evidence for the fundamental role of relationship quality in order to profit from mentoring. Results also indicated that mentoring is not a one-size fits all approach. Moreover, youths’ needs in mentoring may vary along their life stage and intra-individual needs. To conclude, this dissertation illustrates how youths’ social networks and their well-being can benefit from a formal mentor, and offers suggestions of how mentoring can equip youth with skills and competences that outlast the mentoring relation.