Correlational research suggests that emotion regulation deficits, which are known risk factors for substance addictions, may also play a role in the development of problem behaviors such as excessive or maladaptive use of social networking sites (SNS). This study sought to experimentally assess the hypothesized emotion regulatory function of SNS use. 139 undergraduates (53.2% female) were randomized to view brief movie clips known to reliably induce positive (37.4%), negative (29.5%), or neutral mood (33.1%) and then to browse a SNS (46.8%) or control website (53.2%). Mood and subjective urge to access SNS and the Internet were assessed before and after viewing the movie clips and browsing the websites. Participants meeting criteria for “moderate” levels of disordered SNS use self-reported significantly greater deficits in emotion regulation (p = .02, ηp2 = 0.14). Increases in positive and negative affect following the mood induction were associated with a decrease in subjective urge to access SNS (r = −0.22, p = .02, r = −0.28, p = .002, respectively). Time spent browsing SNS resulted in significantly greater increases in self-reported positive affect, compared to the control website (p = .001, ηp2 = 0.09). We replicate previous findings of greater emotion regulation deficits in individuals endorsing problematic SNS use. Increased positive and negative affect resulted in decreased urge to access SNS, suggesting that social networking may primarily serve to counter low-arousal emotions like boredom. Data provide initial experimental evidence to support the hypothesized emotion regulatory function of SNS, with SNS exposure resulting in increased positive affect. Findings suggest that interventions targeting problematic SNS use should incorporate strategies for improved emotion regulation.