Building a new social network (SNS) with connections is especially important for first‐year students to deal with the transition to college. The goal of the current study was to investigate the link between congruence in extroversion and the interaction frequency within cross‐sex classmate dyads on SNS. Based on a cross‐sectional study among 371 cross‐sex first‐year students dyads (Mage = 18; SD = 2.08) using polynomial regression with response surface analysis, we found that: (i) dyads with congruent levels of extroversion indeed interacted more frequently online than dyads with incongruent levels of extroversion; (ii) extroverted dyads interacted more frequently online than introverted dyads; and (iii) dyads with an increased level of incongruence on extroversion had a decreased frequency of online interaction. The sex‐segregated social network might be magnified by the difference in extroversion within cross‐sex dyads. The discussion focused on potential explanations from the reward of interaction model and the expectations for cross‐sex friendship.

BACKGROUND Freshmen were found to use social networking sites (SNS) as a useful medium to effectively adjust to college life, which hints at a tendency to resort to SNS for social compensation. However, the compensatory use of SNS is usually problematic. OBJECTIVE This study explores why a subgroup of freshmen developed depressive symptoms while socially adjusting to college by investigating the antecedent role of introversion, the explanatory role of compensatory use of SNS, and the protective role of perceived family support. The study is among the first to point out the relevance of the compensatory use of SNS in explaining the indirect association between introversion and depression with a longitudinal design. METHODS A 3-wave panel sample of freshmen (N=1137) is used to examine the moderated mediation model. RESULTS We found that introversion at Wave 1 positively predicted compensatory use of SNS at Wave 2 and subsequently increased depression at Wave 3 (unstandardized B=0.07, SE 0.02, <i>P</i>&lt;.001, 95% CI 0.04-0.10; unstandardized B=0.09, SE 0.01, <i>P</i>&lt;.001, 95% CI 0.06-0.12). The moderated mediation model further examined the buffering role of perceived family support within the link between introversion and compensatory SNS use (index=0.0031, SE 0.0015, 95% CI 0.0003-0.0062). Unexpectedly, we found that family support in Wave 1 decreased compensatory SNS use for less introverted freshmen in Wave 2 and further decreased depression in Wave 3. CONCLUSIONS Unexpectedly, our findings uncover an enhancing effect, rather than a buffering effect, of family support by embedding its effect within the relationship between introversion and compensatory SNS use. Appreciating the differences in the casual pathways for freshmen with different levels of introversion clarifies how SNS affect young adults' lives.