American adolescents have experienced growth in their use of online communities; yet, it was unknown whether the current understanding of online-community design applied to the design of communities specific to adolescents. This study bridged this gap, examining (a) How adolescents interact in an online community designed in accordance with existing best practices, and; (b) Whether this understanding of interactions supports the refinement of existing design guidelines or necessitates the creation of new design guidelines to better promote adolescent interaction in an online community? Using a design-science approach, this research investigated an adolescent--centric online community as it progressed through an iterative design. The method involved two broad stages, each consisting of a build/evaluate cycle of an online-community artifact. In the first stage, an online-community for adolescents was created and evaluated in accordance with existing design guidelines. Self-reflection and identity development were two categories of interaction discovered that were not indicated by the guidelines. Theories of psychosocial and cognitive development helped understand the conditions in the community that enabled these interactions and were incorporated into refinements to the design guidelines. These were used to inform the design of a new community intended to promote self-reflection and identity development. This redesigned community was compared to the online community from the first stage (designed around existing best practices). Results revealed an increase in the number of adolescents engaging in desired interactions. This research provides a refined set of design guidelines that inform designers on how to create deeply engaging online communities for adolescents that support the cognitive and psychosocial developmental needs of their members. [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.]