Social Anxiety Disorder (SAD) and, more generally, social fears are common in young people. Although avoidance behaviors are known to be an important maintaining factor of social anxiety, little is known about the severity and occurrence of avoidance behaviors in young people from the general population, hampering approaches for early identification and intervention. Symptoms, syndromes, and diagnoses of DSM-5 mental disorders including SAD were assessed in a random population-based sample of 14-21-year-olds (n = 1,180) from Dresden, Germany, in 2015/2016 using a standardized diagnostic interview (DIA-X-5/D-CIDI). An adapted version of the Liebowitz Social Anxiety Scale was used to ascertain the extent of social fears and avoidance. Diagnostic criteria for lifetime SAD were met by n = 82 participants, resulting in a weighted lifetime prevalence of 6.6%. Social anxiety was predominantly reported for test situations and when speaking or performing in front of others. Avoidance was most prevalent in the latter situations. On average, anxiety and avoidance first occurred at ages 11 and 12, respectively, with avoidance occurring in most cases either at about the same age as anxiety or slightly later. In the total sample, lifetime prevalence for most DSM-5 disorders increased with the severity of social anxiety and avoidance. Results underline the need for preventive or early intervention efforts especially regarding test anxiety and fear and avoidance of speaking in front of others. These situations are particularly relevant in youth. Avoidance behaviors may also be discussed as diagnostic marker for early case identification.