Background/Objectives: Sexuality is part of everyone’s life, especially during adolescence, when young people are discovering themselves and experiencing several changes. Adolescents need to be informed about their sexuality, so they seek and receive information about it from a variety of sources and on different topics. This systematic review aimed to synthesize studies that explored the sources adolescents use and topics they search for. Methods: Quantitative, qualitative, and mixed articles published in Portuguese, Spanish, or English and with respondents aged between 12 and 20 years were included in this study. To fulfill the proposed objectives, three online databases (EBSCOhost, PubMed, and Web of Science) were used, including a total of 48 studies. Results: The most common sources of information are family, friends, school, and the Internet, depending mainly on the reliability of the source and the anonymity when using it. The main topics adolescents search for are sexual intercourse, contraception, relationships, and LGBT issues, since these are less addressed topics. Conclusions: These results are useful in a practical way as a basis for the development of sex education programs that correspond to the needs of adolescents, since they allow us to know which information they are looking for and the sources from which they can receive it.