Internet-based interventions have potential to reduce HIV and STD transmission among men who meet male sexual partners online. From November 2009 to May 2010 we surveyed dating and hook-up website users (n = 3,050), website owners (n = 18), and health department HIV/STD directors (n = 81) to identify structural and behavioral prevention interventions that could be implemented online and which a majority of website users were willing to use, owners were willing to implement, and HIV/STD directors perceived to be effective. A majority of each of the three stakeholder groups agreed on the following: (1) automated HIV/STD testing reminders, (2) local STD test site directories, (3) links to sex-positive safe sex videos, (4) access to sexual health experts, (5) profile options to include safer sex preference, (6) chat rooms for specific sexual interests, (7) filtering partners by their profile information, and (8) anonymous e-card partner notification for STD exposure. Findings help build consensus about how to prioritize resources for implementing online HIV and STD prevention interventions and highlight differences between stakeholders to guide future discussion about how to advance prevention efforts.