Social media offers youth a virtual platform to build community with those who share similar experiences. Moreover, it provides opportunities for marginalized teens' voices can be heard, valued, and privileged. Using case study methods, I examined how marginalized youth used social media platforms to engage in autonomous and agentive literacy practices in online contexts to advocate for social justice. In particular, this multi-case study examined six individual teens, the cases in the study, through a cross-case analysis of their social media literacy practices centered on their racialized experiences in their lived worlds across platforms such as Instagram, Twitter, TikTok, and YouTube. This research also positions youths' engagement in online literacies as part of the intricate identity work of minoritized youth. Findings show that teens enacted literacy practices in social media spaces, related to their racialized experiences and unique perspectives as young people of color in similar, different, and contradictory ways, which shaped their identities, shown through cross-case themes: (1) "More Than Race: Marginalized Teens' Intersectionality in Social Media Spaces"; (2) "Activism, Action, and Allyship: Marginalized Teens' Social Media use Meets Social Justice Movements"; and (3) "We the People: Marginalized Teens use Social Media to Rewrite the Law of the Land Through Equity, Justice, and Antiracism". Thus, this research holds the potential for contributing to what literacy educators and scholars know about how teens of color navigate social media spaces using literacies in ways that promote their autonomy and agency. Implications include suggestions to teachers for privileging multimodal literacies, cultivating opportunities for youth to write for change in online spaces, fostering opportunities for youth to engage as advocates, having critical conversations surrounding race and the racialized experiences of BIPOC individuals, and engaging in antiracist teaching grounded in inclusive literacies and equity and socially just practices. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]