The introduction of advanced technology and mobile instant messaging has constituted a novel social milieu which creates opportunities for individuals to initiate interactive and informative communications. Despite the benefits, negative consequences of social media use have been determined, some of which were presented through matters of concerns including isolation, information leaking, social media reliance, and mental devastation. The current study aimed to examine different types of concerns, namely fear of missing out (FoMO), compulsive usage, and privacy concerns, predicting LINE users' motivations for information sharing intention and information sharing behavior. The data was collected from 562 LINE users with sharing experiences in Thailand. The results of the confirmatory factor analysis (CFA) manifested that all adapted constructs were adequately reliable and valid. The structural modeling analysis (SEM) further revealed that only FoMO and compulsive usage influenced LINE users' motivations for information sharing intention which in turn influenced their information sharing behavior. However, the three types of concerns did not have a direct relationship with information sharing behavior. In addition, when different types of shared information were examined, greeting messages significantly influenced information sharing behavior. The findings also yielded implications for understanding the roles of concerns on sharing information via mobile instant messaging (MIM).