Cyber Security is the right path to go. It is the future now with AI developing. With the technology uprising you will be able to have a career and pursue your goal in preventing sex trafficking online. This career will teach you many skills. I don't think you will be able to get the skills you need in a major in social work or criminal justice. Of course you can always get a minor degree in Criminal Justice to have a grasp idea of how agencies have a process in combating sex trafficking online.
In this major, with the technology out there you will be able to create algorithm platform that could help law enforcement and agencies (ex. FBI) all over on tracking down sex trafficking online. What I mean about platforms is you would be able to create a system online that would look for clues, patterns about a person that is missing or being used for sex trafficking. There are career jobs that need people with Cyber Security skills. Of course if you decide to pursue this path their are certifications that could help you. Below are a list of URLs that would help you.
https://www.comptia.org/certifications - Security+ and others.