Young men who have sex with men (YMSM) are at alarming risk for HIV acquisition, demonstrating the highest rates of incident infection of any age-risk group. GRINDR is a global positioning service-based social networking application popular with YMSM for sexual partnering. To assess the characteristics of YMSM who use GRINDR, we conducted a computer-assisted self-interview-based survey of 375 YMSM using GRINDR in metropolitan Los Angeles, recruited using the GRINDR platform. The median age was 25 (interquartile range, 22-27) years old, 42.4 % caucasian, 6.4 % African American, 33.6 % Latino, and 14.1 % Asian/Pacific Islander. Participants reported high rates of sexual partnering and unprotected anal intercourse (UAI). The majority (70 %) of those reporting unprotected anal intercourse reported low perception of HIV-acquisition risk. Of the participants, 83.1 % reported HIV testing within the past 12 months; 4.3 % had never been HIV tested. Of the participants, 4.5 % reported HIV-positive serostatus; 51.7 % indicated that they would be interested in participating in a future HIV prevention trial. Latinos were more likely than either caucasians or African Americans to endorse trial participation interest (odds ratio, 1.9; 95 % confidence interval [1.1-3.3]). HIV-positive test results were associated with increased number of anal sex partners in the past 3 months (adjusted odds ratio (AOR), 1.53 [0.97-2.40]), inconsistent inquiry about partners' serostatus (AOR, 3.63 [1.37-9.64]), reporting the purpose for GRINDR use including "friendship" (AOR, 0.17 [0.03-1.06), and meeting a sexual partner in a bookstore in the past 3 months (AOR, 33.84 [0.99-1152]). Men recruited via GRINDR were high risk for HIV acquisition or transmission and interested in clinical trial participation, suggesting potential for this method to be used for recruitment of YMSM to HIV prevention trials.