Real Estate Hacks - Most of the members of this group are Canadian real estate agents.  It's known to be one of the biggest Canadian real estate groups.

Real Estate Mastermind - Over 220K members, is known as one of the biggest real estate groups in all of North America.

Lab Coat Agents - Another bigger group.

Follow Up boss Community - Specifically a group for follow up boss users but you will find some great real estate conversations in there as well.

Bosnian Real Estate Group - One that I have to mention for personal reasons, it's a small group but one close to my heart.  If you are anywhere from the Balkan region and are a real estate agent in North America it's a great group of people to join.