Internet addiction takes on different forms and is an important issue for diagnostic and preventive reasons. This paper sets out to diagnose the scale of problematic use of Internet (PIU) in the context of symptoms and mechanisms of FOMO (Fear of Missing Out). For this purpose, triangulation of the following research tools was applied: Social Media Intensity Scale, Fear of Missing Out Scale, Summary of Social Media Use, Social Media Usage Urges, the Bergen Facebook Addiction Scale. To picture the scale of FOMO and accompanying PIU behaviors, data from 717 students in Sarajevo and Mostar cantons (Bosnia and Herzegovina) were collected. The research was conducted in 2 nd half of 2017. Based on this data, we can see that about 20% of young respondents (average age of 13 years) show several FOMO symptoms, whereas another 30% belong are at risk of being addicted to Internet. The remaining 50% of students are not at risk of IAT. These criteria vary due to lack of unified tools to measure FOMO. However, it has been observed that FOMO is minimized by some forms of leisure activity and does not depend on gender.