This announcement solicits applications for the Special Projects of National Significance Program (SPNS) initiative, Use of Social Media to Improve Engagement, Retention, and Health Outcomes along the HIV Care Continuum ¿ Demonstration Sites.  The purpose of this grant program is to support organizations that will implement, evaluate and disseminate findings from innovative methods for identifying, linking, retaining and improving health outcomes for HIV positive underserved, underinsured, hard-to-reach youth and young adults in HIV primary care and supportive services through the use of social media. These methods are expected to include innovative system approaches using a variety of social media technologies or any other internet or mobile based applications, in the engagement and retention in care and viral load suppression of youth and young adults living with HIV.  The innovative system approaches proposed by the applicant organizations must be novel and will be tested and evaluated during the SPNS initiative, though certain components or tools of that system may have already been assessed through other studies. Programs will be expected to implement and evaluate the effectiveness of their models¿ design including service utilization, treatment adherence, cost and impact on health-related outcomes, and to disseminate findings, best practices and lessons learned. Successful applicants will be required to work collaboratively with a HRSA/HAB supported Evaluation and Technical Assistance Center (ETAC) throughout the four year project period. This will include, but is not limited to, the collecting and reporting of data to the ETAC for a comprehensive multi-site evaluation, and the dissemination of successful models to the larger public health community.