As publics witness the COVID-19 pandemic predominantly online, the mediation of digital technologies shape how they perceive, experience, and evaluate the crisis. We conceptualize digital witnessing to characterize these mediated forms of witnessing emerging from the interplay of assemblages of actors, texts, and technologies governed by the affordances and logics of digital media. We draw from Frosh and Pinchevski’s (2014) theorization of witnessing as an assemblage and Frosh’s (2019) world-witnessing to examine the network #MassTestingPH, which consolidated calls by Twitter publics to conduct mass testing in the Philippines. Through a three-level analysis using social network analysis, content analysis, and semantic network analysis of over 70,000 tweets, our findings illustrate the reconfiguration of witnessing processes by indefinitely subjecting witnessing networks, discourses, and assemblages to redirection, reembodiment, and resignification. We argue that this renders digital witnessing the capacity to reproduce multiple meanings, to reconstruct witnessing events, and to redefine power relations. This research advances theoretical and methodological approaches to witnessing research in contemporary media.