This study investigates what social and psychological factors are driving social media usage. The study focuses on hedonic and utilitarian behavior with constructs from games and psychology, the Technology Acceptance Model (TAM), and shopping behavior that are then used to develop a revised model of TAM. The empirical study was conducted in the US and China among college students. Three different models are constructed and the composite model has a high r-square. A comparative analysis is conducted as to the extent to which these constructs play roles in the two populations. The results indicate that in general US students enjoy a greater sense of flow and fun while using social media and have a stronger intention to use it in the future.