It is important to examine gaps in online health-related activities (OHAs) between socially advantaged and disadvantaged groups, considering that emerging information and communication technologies may bring about social disparities in their adoption and possibly expand preexisting health disparities. We thus examined whether digital divide occurs in the area of OHAs, including engagement with a very recent technology. To be more specific, we explored the effects of education, income, and race/ethnicity on OHAs, such as online health information seeking, social media use for health, and health information technologies (HITs) utilization. Moreover, given the importance of socio-contextual factors in digital divide, we examined how social support interacts with education, income, and race/ethnicity, and jointly influences OHAs. Using data from the 2017 Health Information National Trends Survey, we found the effects of education on several OHAs. Income only affected HITs utilization that had just started to diffuse across the U.S. society. We also identified reinforcing effects of social support and education on HITs utilization, and reinforcing effects of social support and income on online health information seeking. The implications of these findings for health communication and public health research were discussed.