I belong to a kidlit crit group that's been meeting weekly for over 4 years. We meet online and have had members from all over the world at one point or another. Like with a writing critique group, finding great partners is key. Also, a match in skill level and goals seems to be important.
I belong to a more informal fantasy artist group as well, not a critique group, per se, more like a support group. We meet randomly in Google Hangouts and have a painting session. If someone asks for a critique, advice is offered.
The kidlit group actually was a result of the #kidlitart chats on Twitter. After one Thursday chat, people kept contacting Bonnie and me (we were the original hosts) and we collected a list of people and times they wanted to meet. At the beginning, I think we coordinated the set-up of 9 critique groups with 5 or 6 members each. I'm not sure what happened to them, but I do know my current group has only 2 of the original members, and about a year after first founding all the group, we blended 2 groups together. The other current members have joined over the years, the newest member, less than year ago. Others left and have gone on to get agents, book deals and awards.
With any relationship, it takes work. All the members must be willing and able to put the work into the group or it just fades away.