How are technologies are designed and used tactically by activists? As the HCI community starts to contend with social inequalities, there has been debate about how HCI researchers should address approach this type of research. However, there is little research examining practitioners such as social justice activists who confront social problems, and are using technology, such as mobile phones, blogging, and social media to do so. In this dissertation, I build on this knowledge within the context of a social movement organization working to stop street harassment (harassment towards women and minorities in public) called Hollaback (ihollaback.org). I position myself as an action researcher doing research and building technologies such as mobile apps and a blogging platform to collect stories of harassment and to support activists. The organization has collected over 3000 stories and represents 50 different locales in 17 countries. Through a series of studies, I examined how technology impacts the organization, activists, and those who contribute stories of harassment. I found evidence that the storytelling platform helps participants fundamentally shift their cognitive and emotional orientation towards their experience and informs what activists do on the ground. My results suggest that doing activism using technology can help remove some barriers to participation but can also lower expectations for the amount of work required. I also looked at how different social media tactics can increase the number of followers and how traditional media plays a role in these tactics. My work contributes theoretically to the HCI community by building on social movement theory, feminist HCI, and action research methodology. My investigation also sheds light empirically on how technology plays a role in a social movement organization, and how it impacts those who participate. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]