This report reviews recent literature on youth recruitment to criminal, terror, and hate organizations within the context of Meta's Tier system to help understand the dynamics of youth recruitment into Tier 1 DOIs and provide actionable insights for platforms’ efforts to enforce against content and actors involved in DOI recruitment. A case study from each DOI category is provided to highlight the recruitment processes at stake; these are the Islamic State, 764, and cartels. Finally, recommendations for on-platform prevention campaigns and approaches are provided.