Recruitment for Voluntary Video and Mobile HIV Testing on Social Media Platforms During the COVID-19 Pandemic: Cross-Sectional Study - Piao-Yi Chiou; Wei-Wen Tsao; Chia-Lin Li; Jheng-Min Yu; Wen-Han Su; Zhi-Hua Liu; Cheng-Ru He; Yu-Chun Chang; Yi-Hsuan Tsai (Journal of Medical Internet Research)