This study aimed to (1) examine receiving, engaging, and sharing behaviors among older adults in the study community who used a health-related closed platform, (2) analyze factors influencing these behaviors, and (3) develop and evaluate the Receive–Engage–Share (R–E–S) structural model. An explanatory sequential mixed-methods design was employed. The sample comprised 45 adults aged 60 years and older in Mae Pu Ka Subdistrict, Chiang Mai Province, purposively selected from an active community health LINE group. The questionnaire showed an Item-Objective Congruence (IOC) range of 0.87–1.00 and Cronbach’s alpha of 0.898. Quantitative data were analyzed using partial least squares structural equation modeling (PLS-SEM), with 2,000 bootstrap resamples for significance testing, while qualitative data from focus-group discussions were analyzed using content analysis. The measurement model met the reported criteria for indicator loadings, composite reliability (CR), average variance extracted (AVE), and discriminant validity assessed using the heterotrait-monotrait ratio (HTMT). The structural model explained 38%, 52%, and 61% of the variance in receiving, engaging, and sharing, respectively. Platform trust influenced receiving (β = 0.42), social support influenced engagement (β = 0.37), and media motivation influenced receiving (β = 0.31). Indirect effects on sharing through the mediating variables ranged from β = 0.16 to 0.24. Qualitative findings supported the role of closed platforms as safe communication spaces that encourage health-information sharing. The findings support the R–E–S model as an exploratory framework for designing digital health communication and media-literacy activities for older adults in the study context.