If you are interested in working with teenagers one-on-one, providing therapy, then you will need a degree that prepares you to be licensed to practice. In psychology, that means earning a degree from a program that is accredited by the American Psychological Association. The American Psychological Association is the largest professional organization for psychologists. It provides oversight and approval of applied psychology programs that prepare students to practice as psychologists. Only applied programs in the fields of clinical, counseling, and school psychology are eligible for accreditation, with a few exceptions. Most states require that students receive doctoral degrees from APA accredited programs in order to be licensed as psychologists.
For more information, check out these resources:
Psychology Laws and Licensing Boards in Canada and the United States
Licensure and Certification for Counselors (American Counseling Association)
MFT Licensure and Certification (American Association for Marriage and Family Therapy)