After talking to the staff, I went ahead and started the Trading Post group on the Weasyl forums:

https://forums.weasyl.com/vbulletin/group.php?groupid=37

If you're not familiar with this, it's basically a friendly art competition with different themes each week, originating on Yerf and later continued by ArtSpots. I wrote a full introduction here. You should be able to join once you're logged into the Weasyl forums; let me know if there are any problems.

I don't know exactly when the first TP will start; I basically need to make sure I have all the group functionality set up correctly and such. Hopefully it'll be in a week or two. If you have artist friends (former Yerfers or otherwise) who you think might be interested, please spread the word. :) This is open to everyone regardless of skill level, as long as the rules of the game are respected.

EDIT:
In keeping with the times, I've also created a Trading Post Twitter to let Twitter users know when a TP is starting/finishing, and a Trading Post Tumblr to showcase weekly submissions.

EDIT #2:
I should also take a moment to stress that it's very important that not just we artists are involved, but also our respective audiences. The TP can't happen without a wider voting pool of spectators to provide additional votes in the polls, so if you want to support this, please please let your watchers know, via social media, journals, etc.