This paper examines the role of permanent social communities online in developing the trust of a luxury brand, focusing on the mediating roles of member engagement, community cohesiveness, and perceived influence, and the moderating role of cross-platform interaction. The study was quantitative conducted on a sample size of 355 participants from Riyadh, Saudi Arabia, shows that member engagement and perceived influence make a significant difference in brand trust, while sense of belonging and community cohesion are either negligible or indirect. It was revealed that cross-platform interaction mediates the relationships between engagement, influence, and brand trust. Although this research has certain limitations, such as using cross-sectional data and its sample from only one city, it underlines the necessity to develop active engagement and influence across different digital platforms for the enhancement of luxury brand trust, and it is recommended that future studies investigate other mediators and cultural contexts.