When Sharing Becomes the Norm: How Disclosure Prevalence and Relational Similarity Shape Social Norms on Social Media

Social media constitute norm-rich environments in which user behavior is shaped by continuous exposure to others’ actions and reactions. Self-disclosure seems especially responsive to such cues, making it important to understand how online contexts encourage or discourage sharing. While prior research shows that descriptive and injunctive norms guide disclosure, the relative impact of behavioral prevalence, reinforcement signals such as likes and comments, and relational similarity has not been clearly established. This paper addresses this gap by examining how distinct normative cues shape both visual and written disclosure online. In two preregistered experiments (n1 = 590, n2 = 1,337), we let participants use a simulated but ecologically valid social media platform, allowing us to independently manipulate disclosure prevalence as well as reinforcement via likes and comments. Results show that prevalence of visual disclosure consistently increased descriptive and injunctive norms, which in turn raised disclosure intentions. Written disclosure influenced norm perceptions but not disclosure intentions, suggesting modality-specific dynamics. Similarity decreased reliance on prevalence for norm inference but strengthened the motivational pull of norms once formed. Surprisingly, reinforcement cues had no effect on these dynamics. These findings refine social norm theory by distinguishing norm inference from adoption and highlight prevalence as a stable normative driver. Practically, they raise concerns about vulnerability to visible peer behaviors and the spread of risky online trends.