Understanding the motives behind people’s interactions online can offer sound bases to predict how a social network may evolve and also support a host of applications. We hypothesize that three offline social factors, namely, stature, relationship strength, and egocentricity may also play an important role in driving users’ interactions online. Therefore, we study the influence of these three social factors in online interactions by analyzing the transitivity in triads or three-way relationships among users. Analyzing transitivity through the lens of triad census for four popular social networks, namely, Facebook, Twitter, YouTube and Slashdot, we find that: (i) users’ interactions are largely influenced by intermediary relations, which enhances the mediators’ stature; (ii) the strength of offline relationships plays a salient role in transitivity of relations online; and (iii) egocentricity, embodied in over-active and popular users, has a significant effect on the dynamics of online interactions.