Loneliness is a complex feeling associated with socio-emotional adjustment difficulties, particularly during adolescence. Such construct is often treated as unidimensional rather than multidimensional, moreover, studies consisting of both peer and family contexts, are very scarce. Adopting a multidimensional and person-centered approach, our study aimed to identify distinct clusters of adolescents with similar patterns of social and emotional loneliness with peers and family and to examine their differences in peer reported social adjustment, controlling for sex. Self-report and peer nomination data were collected from 691 participants (48.36% boys) aged between 11 and 16 years (M = 12.95, SD = 1.15). After controlling for age and preference for solitude, results revealed four clusters with specific configurations of loneliness forms and with different associations with positive or negative features of social adjustment to peer group. Two clusters exhibited adaptive profiles (lower vulnerability to maladjustment): less-lonely, and family-related loneliness profile, in which adolescents were viewed by peers as exhibiting more prosocial behaviors. The other two clusters displayed maladaptive profiles (higher vulnerability to maladjustment): more-lonely, and peer-related loneliness profile, in which adolescents were more likely viewed by their peers as socially withdrawn, peer-excluded, and peer-victimized. Additionally, our results revealed sex differences, with girls in the more-lonely profile showing significant higher social loneliness related to peer group, and higher social and emotional loneliness in family context. Our results highlight the importance of recognizing different forms of loneliness given the differences in adjustment to social contexts observed, shedding further light on this complex construct.