Although workplaces can be supportive environments for creating meaningful relationships, anyone, even on the best teams, can still experience feelings of loneliness at work from time to time. However, current understandings provide only a limited account of workplace loneliness and its consequences in organizations. Therefore, developing a more comprehensive understanding of workplace loneliness would not only add theoretical value but also have practical implications. By integrating the regulatory loop model of loneliness and social compensation theory, we develop and test an expanded model that examines the online and offline performance implications of workplace loneliness. Using a multi-method approach that involved an experiment in the United States and an experience sampling study in China, we found that workplace loneliness can lead to an offline-to-online transition and have negative effects on employee performance. Specifically, feeling lonely at the workplace can hinder employees’ progress towards work goals (work goal progress) by leading to offline work frustration. Additionally, feeling lonely can heighten Internet presence and lead to spending time on non-work-related activities online (cyberloafing) because the Internet can provide a sense of elevated social presence for those who feel lonely. We also found that employees with higher trait adaptive coping for loneliness are less likely to engage in this offline-to-online transition.