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Although face-to-face social contact decreased during the COVID-19 pandemic, some people remained active in traveling and physically meeting as a group to gain benefits like sustaining intimacy and increasing productivity. These group-based activities indicate the necessity of some essential physical meetings despite high risks of virus infection from physical contact amid the pandemic. To balance the benefits of these meetings with the risks and consequences of infection, more should be done to understand the characteristics of physical social contacts and interactions before and amid the pandemic. Using multiday continuous smartcard data, we identify patterns of intentional group travel in the Hong Kong Metro system. These patterns serve as our proxies for physical (visible) interactions and social (invisible) contact networks among people who intentionally travel as a group (ITG). We measure the spatial centrality of ITGs and persistent group riders (PGRs), a subset of ITGs remaining active amid the pandemic, to infer social interactions among metro riders across different locales. By examining the social network formed by the ITG members across time, we found that its size and interconnections varied during the pandemic, and PGR members might be influential vertices in maintaining the networks’ topological properties. The findings could facilitate transit-usage-and-virus-spread modeling and the formulation of more effective pandemic countermeasures in transit-reliant cities.