Online psychoeducation about social anxiety, evidence-based treatments that target social anxiety, and treatment referral/resource information.

Affective attitudes toward seeking treatment for social anxiety were assessed using a standard 7-item 1-7 semantic differential scale in which participants rated "seeking treatment for social anxiety in the next month would be" according to opposite adjective pairs (e.g., "Unhealthy"/"Healthy"). Possible scores range from 7-49, with higher scores indicating more favorable attitudes toward seeking treatment for social anxiety.

As the existing literature lacks a sufficient and specific scale for assessing intentions to seek treatment, we developed a scale based on the Theory of Planned Behavior (https://doi.org/10.1016/0749-5978(91)90020-T) as well as crucial steps toward seeking treatment identified previously (https://doi.org/10.1016/S0887-6185(02)00259-1). The resulting scale includes 13 total items assessing intentions to seek treatment for social anxiety in the following month. Items were rated using Likert scales from 1 ("strongly disagree"/"not very likely") to 7 ("strongly agree"/"very likely"), with higher scores indicating greater intention to seek treatment for social anxiety within the following month.

Paralleling the intentions scale above, the present study developed a measure of perceived behavioral control regarding seeking treatment for social anxiety, as the existing literature lacked a sufficient and specific measure. The resulting scale includes 14 total items assessment perceived ability to seek treatment for social anxiety in the following month. Items were rated using Likert scales from 1 ("strongly disagree") to 7 ("strongly agree"), with higher scores indicating greater perceived ability to seek treatment for social anxiety.

Checklist of behavioral steps toward seeking treatment within specific domains (i.e. in-person treatment, bibliotherapy, online-treatment, medication, and alternative treatments). Because the existing literature lacks a treatment-seeking behavior questionnaire, we developed a behavioral checklist adapted from Buckner and Schmidt (2009; doi: 10.1016/j.brat.2009.04.009). The measure included 19 total treatment-seeking behaviors across the above listed domains, and as such scores could range from 0 (no steps taken toward seeking treatment since intervention) to 19 (every listed step toward every type of treatment taken since the intervention). Higher scores are considered the better outcome in the present study.