Republic of Korea introduced the de facto population concept as the basis for tourism-driven revitalization policies in response to the local extinction crisis. This study uses a systems thinking approach to analyze how over-commercialization and nightlife expansion in Yangyang’s surf beaches have reshaped de facto population structures and community dynamics. Surf tourism has increased the short-term de facto population but failed to attract settlement-oriented residents, creating negative feedback loops that undermine sustainability and community support. Five leverage points―seasonal business stability, community vitality, nightlife events, nighttime disorder, and littering―were identified, with policy measures including local content, non-nightlife programs, responsible behavior, and co-prosperity zones. The study highlights how surf tourism-driven population flows affect regional sustainability and provides insights for policy design in tourism-dependent rural areas.