Although you can find free groups on Facebook, the best groups will cost you money. This is because they only want serious bloggers in the group.
You can find mastermind groups all over the web. Facebook is a great place to start, but ask your blogging friends on Twitter. You might already know someone in a group!
Every group is different. Some just offer advice and support, while others offer a plethora of tools that will help you grow your blog
You get what you pay for. The best groups are paid, and they offer the most value for their members. The group I'm in offers SEO tools, coaching, plugins, and syndication opportunities.