Ongoing advancements in technology have dramatically changed the disclosure media that companies adopt. Such disclosure media have evolved from traditional paper-based ones to the internet as the new platform for disclosing information on companies’ designated websites; however, the new media for disclosures are currently social media platforms. Among the important disclosures that companies make are Corporate Social Responsibility (CSR) disclosures. These are now deemed indispensable due to growing social awareness among societies. While a significant body of the literature is dedicated to studying CSR disclosures and their determinants on the traditional media, studies examining CSR disclosures on social media are quite few. Hence, the aim of this paper is to investigate corporate social media accounts for CSR disclosures, as well as identify their determinants. The sample of the study is comprised of tweets posted on the Twitter accounts belonging to the FTSE 350 constituents. Topic modeling, an unsupervised machine learning approach, is applied to identify CSR disclosure tweets and regressions are run to identify the determinants of CSR disclosure on Twitter. The utilization of topic modeling to reveal CSR content on social media is considered a new approach to mainstream CSR disclosure literature; as such, this paper examines the new phenomenon of CSR disclosures on social media using new research methods. Results show that the popularity of Twitter as a CSR disclosure platform has risen significantly over the past few years. The paper also provides evidence that the presence of women on company boards, especially non-executive women, is positively associated with the extent of CSR disclosure on Twitter. Results highlight the importance of board independence for CSR disclosure in a social media disclosure context, complementing other disclosure platforms. Larger firms are also found to disclose more CSR information on Twitter compared to smaller ones indicating that firm size plays an important role determining a company’s level of CSR disclosure on social media.