The discussion has come up again in the Ravelry forums… Last year I spent hours making a list for the Crochet on Ravelry Group containing all the groups (at the time) that focused on crochet. We had a tricky time posting this list on the Ravelry site, so here it is! https://evenhoward.wordpress.com/crochetgroups/
It is alphabetical. For easy use, please keep another window open and be signed into Ravelry. Please post in the comments if you have updates.