Social media has significantly reshaped the way businesses interact with customers by providing cost-effective marketing solutions which are particularly advantageous for newly established ventures. Despite these opportunities, start-ups continue to face high failure rates with estimated at 90 percent globally and 60 percent in Malaysia within the first five years where often due to persistent marketing challenges. In Sabah, a developing region in East Malaysia characterised by a growing entrepreneurial ecosystem which many start-ups encounter difficulties in effectively utilising social media to enhance brand visibility and foster customer engagement. This study explores the determinants of social media usage among start-ups in Sabah through the lens of the Unified Theory of Acceptance and Use of Technology 2 with particular attention to two central constructs namely facilitating conditions and habit. Additionally, e-satisfaction is examined as a mediating variable to assess whether satisfaction with social media usage influences the relationship between these predictors and actual usage behaviour. To empirically investigate these relationships, a quantitative survey was administered to 87 start-ups operating for less than five years. The analysis tested seven hypotheses. The findings indicate that habit has a statistically significant effect on social media usage, whereas facilitating conditions do not directly impact usage behaviour. Importantly, e-satisfaction serves as a key mediating factor with fully mediating the relationship between facilitating conditions and social media usage, while partially mediating the link between habit and usage. These findings underscore the critical role of internal behavioural factors and user experience over the mere availability of technological resources in driving the usage of digital platforms. From a practical standpoint, the study advocates for the integration of social media practices into daily business operations, the enhancement of digital competencies through training and the implementation of automation tools to support sustained engagement. The study further contributes to the Unified Theory of Acceptance and Use of Technology 2 theoretical framework by reaffirming the central importance of habit and e-satisfaction in influencing technology adoption, thereby offering valuable implications for entrepreneurs, policymakers and digital strategists working to promote start-up sustainability in developing regions.