BACKGROUND: Social support from colleagues is a key resource for employees and organizations, with beneficial effects on performance, employee well-being and resilience. Although the importance of social support is well-known, the factors that help to build and maintain social support are not equally well understood. OBJECTIVE: This study analyzes the impact of workgroup characteristics (i.e., workgroup composition regarding national diversity and tenure; workload) and the COVID-19 pandemic on employees’ perceptions of instrumental and emotional support, and examines the mediating role of informal interactions. METHODS: The study is based on responses from 382 seafarers to a cross-sectional online survey. Hypotheses were tested using OLS regression and mediation analysis using PROCESS. RESULTS: Workgroup composition regarding national diversity had indirect effects on social support through informal interactions around social foci (here: joint leisure activities). High workload and pressure from the COVID-19 pandemic reduced interactions around social foci, thus contributing to the erosion of perceived social support. CONCLUSION: The findings provide insights on the development of social support, suggesting that informal interactions provide an important mechanism for the development of social support at work. From a theoretical perspective, this highlights the value of a relational perspective on the development of social support, a perspective that is based on the insight that social support is embedded in social relationships. From a practical point of view, this indicates that organizations can proactively foster the development of social support through practices that shape workgroup characteristics and social foci.