Copyright infringement on designs?

[Sephiroth]

I created a toon design called "Ermen Vehn Buran". I been noticing other people using my design as a base for theirs and virtually not changing anything but the color plus a few features such as beards. I am fine with this, but I noticed an actual DJ group is now using my base design for their profile picture. Kheiro & Medi is the group that duplicated my design and changed the color of both. Adding just a few features like beards. So in short I am just wondering if this is enough for potentially enforce copyright laws onto them? Such as if they release a song or merchandise with that design on there. Or if it obviously helps them generate revenues?

I also disclosed a copyright statement in my about section from a few months ago when I created the design.
https://www.facebook.com/ermen.vehnburan

https://www.facebook.com/KheiroandMedi

[bcnu]

Creating a derivative work of a copyrighted design is the exclusive right of the copyright owner (i.e., you, the artist). Violating the copyright law means they can be sued immediately upon your registration in the US Copyright Office. 17 USC 511, 504. Statutory damages of up to $150,000 for willful infringement (i.e., there was copyright notice or they otherwise KNEW it was copyrighted and copied it anyway).