In this paper key trends in the development of extremist and near-extremist youth subcultures are outlined, and characteristic features of criminal and near-criminal youth organizations are described. The results of an empirical study of the activity of existing harmful groups and organizations that are known to involve minors in their ranks are presented, including a description of their dissemination platforms, size and gender composition, declared and actual goals, and external manifestations. Mechanisms for the formation of extremist attitudes in minors are identified, and the special role of psycho-linguistic and forensic  psychological expertise in the investigation of extremist crimes is demonstrated. Recommendations are offered towards the implementation of effective counteraction to extremism among minors.