In both the West and East, social withdrawal, manifested as solitude and shyness, has distinct developmental implications for adolescent mental health. Representative countries in the West (e.g., North America and Europe) and East (e.g., China) were selected to compare cultural differences. This literature review aims to discuss how adolescents experience solitude and shyness differently in North America, Europe, and China from a developmental perspective, and adopts a cross-cultural perspective to explain the distinct outcomes of adolescent social withdrawal. Furthermore, humanistic perspectives are discussed to link adolescent development and humanism in terms of previous empirical evidence and counseling practices. In North America and Europe, solitude has both adaptive and harmful effects on adolescents’ mental health. However, solitude in China and shyness in both cultural settings tend to adversely affect adolescent mental health. These findings from previous studies correspond to developmental perspectives in terms of mental health, personal adaptation, and self-development during adolescence. The strengths, weaknesses, and implications of this literature review are also discussed.