Physical inactivity increases the risk of developing several highly prevalent diseases (cardiovascular disease, diabetes, hypertension, some cancers, and obesity). As large proportions of the population are not meeting physical activity guidelines, increasing physical activity (PA) is a public health priority. As such, intervention strategies that can reach many people in a cost-effective manner are desired. Web-based physical activity interventions have shown promising results and will continue to gain importance through growth in Internet access, but little investigation focus the Internet sites and social networks as information sources on PA knowledge and PA level, comparatively of using other (traditional) information sources. This investigation aims to evaluate differences among the use of Internet sites and social networks and traditional PA information sources, and the influence of each information source on PA knowledge and on PA level. The study included a randomly recruited sample of 200 subjects (53% males; 47% females), age 31.6±12.6 years old. A survey was designed to (1) identify where people find physical activity-related information, considering age, gender and education differences and (2) compare the influence of each information sources on PA knowledge and PA levels. Results show that Internet and social networks present the lowest usage as PA information source (21.5 and 5.0% respectively).The Internet is used as PA information source equally by genders (21.7 males % vs female 21.3%), mainly by and young adults (31.3%), and educated people 31.4%. Social networks are used mainly by males (6.6% vs female 3.2%), young and young adults (8.3 and 6 %), and equally (and less used) be low and educated people (5.5 and 5.7%). Looking for PA information in Internet sites no influence nor in PA knowledge nor in PA level, whereas looking for PA information in social networks show no influence on PA knowledge, but present a positive influence on PA level. This is an important finding, in the sense that the use of social networks as PA information source seems to have a positive impact on embracing an active lifestyle.