Sex trafficking is a current, severe and intense global phenomenon. Many studies have made substantial efforts to map the routes and relations between countries of origin, transit, destination, and the methods of recruitment and retention. With a focus on the role of social relationships, for this article, we conducted a literature review using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) to provide further scientific evidence of the elements and processes that push victims – primarily women and girls – into sex trafficking. The findings show that family, intimate relationships, friendships and acquaintances play a critical role in the pre-entry period before sex trafficking. Among these, family violence, abandonment and abuse emerge as severe risk factors, as well as the role of fraudulent intimate relationships. We also include additional social and individual risk factors that, together with the role of family and social relationships, have impacts on potential victims, increasing the likelihood of sex trafficking.