The rise of social networking mobile applications (apps) (e.g, Grindr, Jack'd) created specifically for men who have sex with men (MSM) has generated public health concerns and conflicting studies about the impact on risky sexual behaviors. This study seeks to gain a more precise understanding of why and how MSM are using social networking mobile apps, and informs the theoretical debate concerning the impact of social networking technology on sexual risk behaviors. A questionnaire survey was conducted, both online and offline, with young MSM app-users in Hong Kong to examine their apps use (frequency, history, and exposure of own face and body) and recent sexual partnering via apps (total sexual partners [TSP] and condomless sex partners [CSP]) in relation to gratifications sought and sexual sensation seeking. The results indicated that finding sexual partners was not a high priority for using MSM apps; surveillance, relationship, and diversion motives were more important while social motive shared similar importance. App-use frequency, sex motive, and sexual sensation seeking predicted more TSP while surveillance motive predicted fewer TSP. None of these variables, however, directly predicted CSP. Sexual sensation seeking in interaction with sex or diversion motive predicted both TSP and CSP. Despite lacking significant association with sex motive or sexual sensation seeking, app-use frequency was a stronger independent predictor of TSP. While frequent app use may facilitate more app-met sexual partners, this study found no evidence indicating that app use promotes riskier sexual behavior with those partners.