If the content stolen lost you money, there is a newly created Copyright Claims Board that is supposed to help give creators an easier way to hold thieves accountable.
To manage the takedown yourself you will need to gather some information and then alert the Internet service provider that is hosting the site infringing on your content.
Gather the following information regarding the website.
The hosting provider
Internet service provider
Owner of the website
Relevant information about the party or parties involved in hosting the content
Draft a DMCA Notice on your own or by using a free template. If writing your own, make sure to include the following:
The subject of your notice
Explanation of why you’re sending the takedown notice
Provide proof of your copyright
Give a good faith statement
Give a perjury statement
Leave your signature and personal information
Send all the gathered information to the internet service provider hosting the site.
When possible, add watermarks to photos that you have behind paywalls. This is usually for creators with Patreons and OnlyFriends accounts. OnlyFriends may watermark their photos, but it is easily cropped – so it’s suggested that you watermark them yourself in a more visible way.
How to Submit Copyright Claims on Various Platforms
YouTube has a DMCA Webform that you can fill out, as well as a Copyright Match Tool to help you find offending content.