Social media activism—posting or reposting ideas, images, or words surrounding different social movements—has swelled in recent years with the growth of the internet. Teenagers have begun using their social media accounts to share their opinions and current events related to issues they deem important. This study had two main aims: to assess factors that influenced high school-aged teenagers’ motivation to post activist content on Instagram, and then to explore how those factors differed between genders. A survey was distributed to students at a midsize high school in Washington state that collected participants’ (n=114) demographic information, willingness to post activist content, and motivation levels to post about five popular issues. Results were analyzed by identifying key themes in qualitative responses and categorizing them using the preexisting Scale of Motives for Using Social Networking Sites (SMU-SNS). It was found that nonbinary and particularly female teenagers were more likely to post activist content than male teenagers. Participants indicated that relation to personal identity, personal/public knowledge on the issue, and perceived severity/importance of the issue were main reasons for posting activist content. Further analysis showed these themes fell under the SMU-SNS categories of Social Connectedness, Information, and Self-expression. These conclusions have great significance for public health organizations and social justice movements looking for teenagers willing to engage in this form of advocacy, suggesting they should tailor activist content for Instagram Stories and that they need to look for alternative ways to get male teenagers involved.