Friendship formation is important to online social network sites and to society, but can suffer from informational friction. In this study, we demonstrate that social networks may effectively use an IT-facilitated intervention -- displaying things in common (TIC) between users (mutual hometown, interest, education, work, city) -- to encourage friendship formation. Displaying TIC updates an individual's belief about the shared similarity with another and reduces information friction that may be hard to overcome in offline communication. In collaboration with an online social network, we conduct a randomized field experiment that randomly varies the prominence of different things in common when a user is browsing a non-friend's profile. The dyad-level exogenous variation, orthogonal to any (un)observed structural factors in viewer-profile's network, allows us to cleanly isolate the role of preferences for TIC in driving network formation and homophily. We find that displaying TICs to viewers can significantly increase their probability of sending a friend requests and forming friendships, and is especially effective for pairs of people who have little in common. We also find that displaying TIC can improve friendship formation for a wide range of viewers with different demographics and is more effective when the TICs are more surprising to the viewer.