This was long overdue, but better late then never.
Up until recently, people would be able to file a report under "My work used" if their work was stolen on deviantART.
Now, that report system has changed, first party copyright reports can now be filed under "My Intellectual Property" giving you, instead of a form to fill out, a link to the updated form asking you to fill out a DMCA report.
The DMCA hyperlink "File a DMCA Notice"
After clicking the hyperlink described in the subscript, you'll need to click ether "Me" or "A company, client, or organization I represent", file out the necessary information.
After clicking the appropriate button (The second button is roughly similar)
After filling out the report, click "Submit Notice"
Q: What if I'm not the copyright holder?
Q: Can't I just file a DMCA report as a third party report?
Q: Is deviantART still accepting third party reports?