While research on online social networks and disasters continues to grow, social scientists know little about how these online networks transform during a crisis and how they drive disaster outcomes. With two original datasets, this study investigates how Houston’s online social network transformed during Hurricane Harvey (2017), and how online social media activity fueled post-Harvey rebuilding. The findings of a social network analysis (N= 2,387,610) reveal the Houston-area online social network grew denser, clustered and more efficient during the disaster. A spatial analysis and three separate regression models of activity before, during, and after Hurricane Harvey confirm that among 333 Nextdoor Neighborhoods, hyperlocal social media activity at every stage accelerated the pace of rebuilding in these geographically based online communities. These findings suggest that policy and decisionmakers should invest into online and offline hyperlocal social networks well before a disaster strikes, and leverage resources and legislation to maintain and strengthen the telecommunications and energy infrastructure that supports access to social media and tech during a time of crisis.