Report Spam/Abuse/Mature/Copyright Infringement/Etc

If it’s on WordPress.com, yes:

https://en.support.wordpress.com/content-theft-what-to-do/
https://en.support.wordpress.com/report-blogs/

If it’s a self-hosted WordPress blog, they are the property and under the control of their respective owner(s), so there’s not much you can do. If the blog violates the hosting provider’s ToS, you could contact the hosting provider. If the blog is posting stollen content, refer to this article:

https://lorelle.wordpress.com/2006/04/10/what-do-you-do-when-someone-steals-your-content/

Sorry, I should of explained better. I’m hosting the website, a multisite, and was wondering if there was a way this could be reported to me on my site.

To force this, you could add an appropriate link into each of the themes you provide.

I’ve heard of a pay-for plugin to do that, but using any contact form plugin can be utilized to that end, I imagine.