Study aim: the purpose of the present study was to survey the impact of a social media platform on physical fitness, physical activity levels and daily sitting time. Material and methods: a total of 2039 users (1445 women and 594 men) of the social media service (HeiaHeia, Helsinki, Finland) voluntarily participated in the study by answering an online questionnaire provided by a survey. Results: about 63.8% of the participants reported that the service has advanced their perceived level of physical fitness, while 36.2% reported no impact on their fitness. Most participants (71.3%) with BMI over 25 reported that the service had helped them to improve their physical fitness. Participants with BMI over 35 reported a more positive impact than in any other weight range groups. One-third of the participants (32.3%) sat for more than seven hours a day; 23.5% sat less than five hours a day. More than half of the participants (56.8%) were encouraged to be physical active during the day and aimed to reduce sitting time at their jobs during the workday. Conclusions: there seems to be a positive impact of web services that promote physical activity on the physical fitness among social media users. Although the present service is not merely well suited for physically active and physical fit users, it motivates users of all fitness levels to exercise. However, more studies are needed to clarify effects of social media on physical activity, fitness and health.