@Riot, What am I supposed to do about ART THEFT?

Excuse me if this post is a little emotional. I won't be naming names and I won't be posting the stolen art.

TL;DR a popular Youtuber stole my art and according to Youtube I can't do anything about it: wat do?

You've seen a cool drawing of a champion in a Youtube video, right? I know you've clicked on a random video just because it had Sona's breasts in the thumbnail. Maybe you didn't realize that someone had to have put a lot of effort into that thumbnail. And I wouldn't fault anyone for this, but a regular Joe/Jane wouldn't notice there was no link to the original art or artist in the video description.

Being an artist myself I have such a problem with that. It's art theft. But I couldn't do anything about it; it wasn't my art. Until it was! OH BOY.

I was mad, and then upset, and then I cried for a long time. And I tried to report it to Youtube (heads up: it's useless, don't bother with all the trouble)

Is there really nothing I can do about this sort of thing? I can't have a video taken down if I don't own the full copyright (art+character.) Can I do nothing? Am I just not supposed to make fanart for this BS community??

(NOTE: not in Community Creations because I'm pretty sure that's just for actual art?) (BIGGER NOTE: before anyone tries to claim such, ART THEFT =/= PUBLICITY if the artist doesn't get publicity thru credit/etc)