Frequent use of websites and mobile telephone applications (apps) by men who have sex with men (MSM) to meet sexual partners, commonly referred to as "hookup" sites, make them ideal platforms for HIV prevention messaging. This Rhode Island case study demonstrated widespread use of hookup sites among MSM recently diagnosed with HIV. We present the advertising prices and corporate social responsibility (CSR) programs of the top five sites used by newly diagnosed HIV-positive MSM to meet sexual partners: Grindr, Adam4Adam, Manhunt, Scruff, and Craigslist. Craigslist offered universal free advertising. Scruff offered free online advertising to selected nonprofit organizations. Grindr and Manhunt offered reduced, but widely varying, pricing for nonprofit advertisers. More than half (60%, 26/43) of newly diagnosed MSM reported meeting sexual partners online in the 12 months prior to their diagnosis. Opportunities for public health agencies to promote HIV-related health messaging on these sites were limited. Partnering with hookup sites to reach high-risk MSM for HIV prevention and treatment messaging is an important public health opportunity for reducing disease transmission risks in Rhode Island and across the United States.