The convergence of social commerce and mobile commerce, harnessed by collaborative technological advancement and innovative users, which has transformed e-commerce platforms into effective instruments that support business strategies and provide consumers convenience. The ubiquitous nature of smartphones and the availability of real-time internet connections drive mobile social commerce. Online consumers are vulnerability to opportunistic exploitation if some parties withhold resources. Effective social interaction requires information transparency and trust. Consumers may depart from their routine buying decisions, which may or may not be the result warranted. Even so, in order to achieve the necessary level of success in online shopping, users must have confidence in their capacity to organise and execute a sequence of actions. This research examined three factors that affect consumers' purchase decision on mobile social commerce, namely social capital, situational influence and technology self-efficacy. A snowball sampling approach was applied in this research to gather responses from the e-consumers in Sabah, Sarawak and the Federal Territory of Labuan by means of WhatsApp, Wechat and email using a questionnaire. A total of 396 samples were analysed using SPSS and SmartPLS software. The assessment of the PLS-SEM structural model demonstrated that social capital and situational influence have a significant effect on consumers' purchase decisions, while trust partially mediates the relationships. Although technology self-efficacy has no direct impact on consumers' purchase decision, it is mediated by trust. This research provides information on the factors which directly affecting consumers' decision using mobile social commerce. Besides depending on AI-based techniques for early detection of fraudulent patterns and outliers for protection, consumers should take the initiative of self-protection during online shopping. Future studies should include psychological and personality characteristics, such as resilience and vulnerability to add to the body of knowledge on mobile social commerce.