This research examines the relationship between social media marketing activities and purchase intention mediated by trust and brand image to confirm the constructs with practical applicability, specifically in a growing online ride-hailing service company. This study employs a quantitative approach with a causal research design to test the proposed hypotheses to identify interrelationships between each pair of constructs. Data collection was performed through a survey of 350 respondents via an online questionnaire as the primary data source distributed to social media users in Indonesia who had experienced using GO-JEK services. In addition, EFA, CFA, SEM, and bootstrapping methods were run to analyze these research data. Social media marketing, trust, and brand image affect consumers’ purchase intention significantly. Among the five dimensions of social media marketing, the findings show that two dimensions—namely, entertainment and word of mouth, bring the most significant direct effect on purchase intention. Trust and brand image mediate the relationship between social media marketing and purchase intention. This study suggests practical directions for organizations. First, it reveals the social media dimensions that directly encourage purchase intention among consumers. Second, it explains that trust and brand image can amplify each variable’s influence on the purchase intention among consumers. GO-JEK is an example of the online ride-hailing industry that causes the generalizability issue in different business contexts. Based on our findings, there are some practical directions for GO-JEK. First, it reveals the social media marketing dimensions that directly encourage purchase intention among consumers to use GO-JEK. Second, it explains that trust and brand image can amplify the influence of each variable on consumers’ purchase intention. Very few studies investigated social media marketing’s role in a GO-JEK business model in the Indonesian context. This research delivers in-depth insights into the significant factors that affect Indonesian consumers to decide which product they intend to buy through the influence of social media activities.