Purpose This paper aims to explore the extent, nature and communication potential of companies’ use of three popular social media platforms (Facebook, X and LinkedIn) to report on sustainability. Design/methodology/approach Qualitative methodology through the use of the netnography approach was adopted to evaluate the use of social media for sustainability communication by the Top 50 ASX companies. Content analysis of all company posts determined those with social and environmental content. A thematic analysis was performed using the global reporting initiative (GRI) framework to examine the nature of the reporting. The media richness framework was used to measure the communication potential of the social media platforms for sustainability communication. Findings The results indicated that the extent of sustainability posts on social media represented less than 20% of total social media posts. The nature of posts by the Top 50 ASX companies was higher on social issues than on environmental issues, which is contradictory to many previous studies. The study also found that while the social media platforms afforded high levels of media richness, most companies failed to exploit the platforms’ full potential to disseminate sustainability information. Research limitations/implications This work provides both empirical and theoretical contributions to the ongoing debate concerning the use of social media for sustainability communication. The paper extends Lodhia et al.’s (2020) study of social media use for legitimation purposes and adapts Lodhia’s (2004) media richness framework to social media for sustainability reporting. It adds empirical insights into social media’s communication potential and value for communicating sustainability information. Practical implications The extent and nature to which organisations use social media to disclose their sustainability performance has significant practical implications for a variety of stakeholders. The results reveal to these stakeholders and the companies themselves the level of utilisation of social media along with the potential that can be harnessed. These results can potentially improve the quantity, timeliness and usability of sustainability reporting using social media platforms. Social implications The study provides valuable evidence to increase understanding of the sustainability social media communication landscape, which organisations can potentially leverage to communicate their messages. Additionally, sustainability awareness is increased across various demographics by disseminating sustainability information to the wider public. This study will assist policy-setters in developing guidance for using social media for sustainability reporting. Originality/value This study extends existing literature, particularly the Lodhia et al. (2020) study, which has primarily focused on examining sustainability content in the media with limited exploration of the communication potential of social media platforms to communicate sustainability content.