Because use of geosocial-networking smartphone applications ('apps') is ubiquitous among men who have sex with men (MSM), online-to-offline service models that include advertisements on these apps may improve engagement with effective HIV prevention and treatment services. Through our formative qualitative study, we conducted individual in-depth interviews (n = 30) and focus group discussions (n = 18) with MSM in Rhode Island to develop a digital social marketing campaign aimed at increasing HIV testing, including how best to reach men by advertising on apps. Qualitative data analysis revealed that participants were frequently exposed to pop-up advertisements on apps. These advertisements are viewed as invasive and, as such, many expressed a preference for other formats (e.g., direct messages, banner advertisements). Men expressed a preference for provocative images and phrases to catch their attention followed with fact-driven messaging to motivate them to engage with services offline. Findings from this study offer several practical recommendations for developing a social marketing campaign that uses advertisements on apps to increase HIV testing among MSM, including using formats other than pop-up advertisements and pairing fact-driven messaging with eye-catching images to direct them to trusted local clinical services.