Ironically, the only piece of art I've ever had stolen.... isn't teeeeeeechnically mine to start with. Let me explain.
I was in a printmaking class in college, and we had to replicate an etching or blockprint by one of the great masters. I chose this image, a griffin by Albrecht Durer:
It was a blown up photocopy from a book, which we transferred onto a linoleum block. I spent 2 weeks carving that sucker, and I was one of the first people in my class to actually pull a perfect print off of their project. I still love this piece.
But, like... it isn't technically mine? I can't claim that I came up with the design, or even re-drew it in my style. It's literally an exercise to copy a masterwork. The original artist made it almost 500 years ago! So it's only sort of mine in that I put in the work to re-carve and print it.
And (also on Deviantart), someone 'stole' it, and someone else let me know about it. And... I dunno, I was a little mad, but... not anywhere near as mad as I would've been had it been one of my original pieces? I'm almost a mixture of relieved and offended that that's my only artwork that's ever been stolen (that I know of).
(Dear Internet: This is not an invitation to steal my artwork. Do not steal my artwork. I will not tolerate it.)