Online reviews facilitate customer brand engagement, but few studies have explored this problem from the perspective of interpersonal attraction and its psychological mechanisms in the social commerce context. This paper aims to investigate the effect of reviewer-reader similarity (including external and internal similarity) in online reviews on customer brand engagement in the social commerce context. Drawing upon the social categorization theory, a conceptual framework was developed and tested empirically. Data collected from a sample of Chinese consumers with the shopping experience on social commerce websites (N=392) was analyzed using Partial Least Square (PLS). Findings reveal that both external and internal similarities are indirectly influenced consumer brand engagement, and mediated by consumers' perceived value and congruence transferred through this process. The impact of external similarity on customer brand engagement was greater through consumers' perceived value, whereas the influence of internal similarity was stronger through consumers' self-brand congruence.