There needs to be more research on how self-image congruence affects consumer outcomes concerning social network site (SNS) brands. As SNSs like Facebook continue to grow, they must position themselves effectively to stand out from their competitors. This study aims to contribute to our understanding of this topic by exploring the mediating effect of self-image congruence on brand personality (BP), brand commitment, and preference for the Facebook brand. We conducted PLS path modelling on data from American millennial Facebook users (N = 512, Mage = 27.1, SD age = 4.9, Female = 52%). In our model, actual and ideal self-image congruence partially mediate the impact of BP dimensions (emotionality and responsible) on brand commitment. The BP dimension activity directly affects brand commitment without mediation, whereas simplicity has no significant effect. Furthermore, brand commitment has a positive impact on preference for the SNS. This study has practical implications for SNSs and marketers who wish to position their brand or use social media as a selling channel.