(1) Summary: Many studies have evaluated the association between traditional media exposure and the presence of body dissatisfaction and body image disorders. The last decade has borne witness to the rise of social media, predominantly used by teenagers and young adults. This study's main objective was to investigate the association between how often one compares their physical appearance to that of the people they follow on social media, and one's body dissatisfaction and drive for thinness. (2) Method: A sample composed of 1331 subjects aged 15 to 35 (mean age = 24.2), including 1138 subjects recruited from the general population and 193 patients suffering from eating disorders, completed an online questionnaire assessing social media use (followed accounts, selfies posted, image comparison frequency). This questionnaire incorporated two items originating from the Eating Disorder Inventory Scale (Body Dissatisfaction: EDI-BD and Drive for Thinness: EDI-DT). (3) Results: We found an association between the frequency of comparing one's own physical appearance to that of people followed on social media and body dissatisfaction and drive for thinness. Interestingly, the level of education was a confounding factor in this relationship, while BMI was not. (4) Discussion: The widespread use of social media in teenagers and young adults could increase body dissatisfaction as well as their drive for thinness, therefore rendering them more vulnerable to eating disorders. We should consequently take this social evolution into account, including it in general population prevention programs and in patients' specific treatment plans.