You will want to report the nude photo(s) or video that someone has posted of you to get them removed from the website. It is a very distressing process and have shared some links below to help you.
Here are some quick links that can help you request that the nude photo(s) or video be removed from Facebook, Twitter, Instagram, Google, Instagram, Yahoo, YouTube, Reddit, Microsoft and more.
http://www.cybercivilrights.org/online-removal/
https://needhelpnow.ca/app/en/removing_pictures-facebook
http://www.womenagainstrevengeporn.com/#!photo-removal/c9fv