PDI is a mobile application aimed at engaging key populations, including people who inject drugs (PWID), sex workers (SW), men who have sex with men (MSM), and transgender individuals, in Harm Reduction services using a social network strategy. The app allows users to share QR-coded coupons, promoting testing for HIV, syphilis, hepatitis B, C, and TB screening, while providing access to preventive goods. Users receive monetary incentives for participation, with a strong emphasis on maintaining the confidentiality and anonymity of collected data, which includes test results and socio-demographic information. A supporting web-based platform facilitates data management, ensuring quick access to datasets and reports. Developed by the ICF Alliance for Public Health with support from the Global Fund, PDI aims to enhance community engagement in health services, focusing on communicable diseases.