Background Older adults were perceived as a vulnerable group during the COVID-19 pandemic due to the health and mental health challenges they faced. The pandemic was accompanied by an “infodemic” of overabundant and questionable information that has affected older adults’ mental health. As the infodemic and ageist narratives were prevalent online, more anxiety symptoms have been induced among older adults who used social media. Age-friendly communication, advocated by the World Health Organization’s Age-friendly City (AFC) guide, could be an antidote by providing tailored information via appropriate channels for older adults. Objective This study investigated the role of community capacity for age-friendly communication in mitigating anxiety during the pandemic. We hypothesized that age-friendly communication would moderate the effects of infection risks and social media use on anxiety. A double-moderating effect was hypothesized in the context of diminished trust in traditional media. Methods Data were collected from a cross-sectional telephone survey conducted in Hong Kong in 2020. Older adults (N=3421, age≥60 years) were interviewed about their well-being and daily lives. Community capacity for age-friendly communication was measured in a living district–based evaluation. It had 2 components: the reach of appropriate information to older adults (AFC-Information) and the age-friendliness of communication technologies (AFC-Communication Technology) in the community. We tested the hypothesized moderation and double-moderation effects with ordinary least squares regressions. Results Perceived COVID-19 infection risk (b=0.002, P=.02) and use of social media for COVID-19 information (b=0.08, P=.04) were associated with more anxiety symptoms. The effect of using social media was moderated by AFC-Information (b=–0.39, P=.002) and AFC-Communication Technology (b=–1.06, P<.001), and the effect of perceived COVID-19 infection risk was moderated by AFC-Information (b=–0.03, P=.002) and AFC-Communication Technology (b=–0.05, P<.001). Lower trust in traditional media exacerbated anxiety symptoms associated with social media use (b=–0.08, P=.02). Higher AFC-Information alleviated this moderation effect (AFC-Information × media trust b=–0.65, P<.001; AFC-Information × social media use b=–2.18, P<.001; 3-way interaction b=0.40, P=.003). Conclusions Our findings highlight the role of community age-friendly communication in mitigating anxiety related to the infodemic. Although using social media may have exacerbated the impact of the infodemic on older adults, it has the potential to deliver timely information for an adequate health response. Although the amplifying effects of low media trust was associated with social media use, age-friendly communication determined its strength. Instead of discouraging the use of digital technologies for COVID-19 information, efforts should be made in tailoring information and communication technologies in local communities for older adults.