To date, little data on pre-exposure prophylaxis (PrEP) users outside of the clinical trial setting are available. A repeated cross-sectional survey of one of the largest social and sexual networking websites for men who have sex with men (MSM) in the United States was conducted in August 2013 (Wave 1) and January 2014 (Wave 2). Multivariable logistic regression models were used to assess factors associated with having heard of and having taken post-exposure prophylaxis (PEP) and PrEP in Wave 1 (N = 4043) and Wave 2 (N = 2737) separately. In Wave 1, 147 (3.6 %) and 61 (1.5 %) reported using PEP and PrEP, respectively, compared to 119 (4.4 %) and 62 (2.3 %) in Wave 2. Higher-risk sexual behaviors were associated with having taken PEP and PrEP, and previous PEP use was associated with having taken PrEP. Understanding factors that are associated with early use of PrEP may help inform wider utilization of PrEP by at risk MSM.