Social media use has proliferated in the past ten years and studies are beginning to investigate the associations of social media use with political movements and mental health. This study extends this literature by testing a novel hypothesis that social resource loss on social media (e.g., “unfriending”) may be associated with increased symptoms of depression and anxiety in social upheaval. A population-based sample of 1,208 Chinese Hong Kong citizens (mean age = 46.89; 52.4% female) was recruited by random digit dialing in February 2015, two months after the conclusion of the Umbrella Movement in Hong Kong. Respondents reported social resource loss on social media, and anxiety and depressive symptoms. Hierarchical regression analyses revealed that social resource loss on social media was positively associated with depressive symptoms but not anxiety symptoms. Age moderated the positive association between social resource loss on social media and depressive symptoms. Simple slope tests revealed that the association was significant only among middle-aged (39–55 years) and older (≥56 years) adults but not younger (18–38 years) adults. The current findings shed light on the role of social media in mental health during political movements across different age groups.