Hello, I'm the person who draw this.
As far as I know what happened, is that some of my works were re-posted to WildCritters from PIXIV, and some of them were hidden in few minutes. (anyone can't see its including WildCritters's member).
Few days later, one of my friend who is WildCritters member (I'm not member) email to the person who re-posted my works to WildCritters. He mentioned that "Spike believes that artist is looking at this website and would delete their work on their pixiv if it's here."
My friend reply the email told him I am happy to see my works been posted on WildCritters, then my works are not hidden anymore.
For other Pixiv artist, I think the only way to find their works is to go to their Pixiv page.
This is my Pixiv : http://www.pixiv.net/member.php?id=2647066
And you can serch WildCritters with keyword : "ヴォルカーノ", you will find my works as well.
Thank you all in KemonoChan