Purpose: The study aims to explore Greek libraries’ social media presence and library operation and social media use during the coronavirus disease 2019 (COVID-19) lockdown. Design/methodology/approach: Primary data were collected via an online questionnaire that was distributed to the Greek libraries. The final sample comprised 189 libraries of all types with the exception of school libraries. Findings: Results indicated that Facebook is the most widely used platform, while social media are mainly used for sharing announcements about library operations and for the promotion of events. During the COVID-19 lockdown, libraries responded quickly to the new circumstances by taking many of their services online. However, they did not fully use social media for service provision but rather used social media as a static communication channel. Only a few of the libraries grasped the opportunity to highlight their role in the promotion of public health by providing timely and reliable information. Practical implications: Library leaders who are looking to harness the power of social media for service promotion and outreach should build a strategy that takes platform popularity, current social media trends, patron preferences and the specific promotional objectives of their library into consideration. Originality/value: To the best of the authors’ knowledge, the current research is the first which attempts to explore the social media presence of Greek libraries of all types and changes made to library operations and social media use in response to the COVID-19 lockdown.