Over the years, I've been part of several online blog support groups. I think the advantages outweigh the negatives, and I've connected with a lot of interesting writers. But, before you join, you need to decide if it is worth the investment of your time and energy.
Promotion - A support network is a great way to promote your blog and writing projects. But you do need to make the time commitment to read and support the other members. It does take time, depending on the size and frequency of the events in your group.
I'm in one group with over 7,000 members. If you comment or post, expect a lot of email. It's a great way to find other writers and see what they're doing with their social media sites. But your inbox will be flooded when everyone comments or posts.
Social Media - This is a great way to increase your social media followers. I like the ones that make following others optional. You tend to get more true followers who stick around. It's disappointing when you get a boost and then a spike in unfollows quickly behind it. That happened to me once, and I learned my lesson.
Feedback and Support - I like to support other authors on their writing journeys, so I enjoy seeing what other bloggers are up to. I also appreciate the hints and suggestions that they make about marketing, social media, and blog content.
How Do You Find a Group? - Search Twitter or Facebook for "Blog Groups." There are a lot of them out there with different rules for membership and engagement. Visit a while before you join to make sure that your work fits. My goal was to increase traffic to my blog, so I chose several that were not book- or author-centric.
If you're willing to commit the time to spend on social media and your blog, then these groups are a good (free) way to promote yourself. If blogging isn't your cup of tea, there are also plenty of Facebook and Twitter groups to promote your books.
Best wishes with your writing projects!