Are you noticing a sharp decline in followers on Google Friend Connect? Don't worry, it's not you. You may just have to do some retooling.
Here is a quote from the Blogger Help Forum, dated 12/21/15.
In 2011, we announced the retirement of Google Friend Connect for all non-Blogger sites. We made an exception for Blogger to give readers an easy way to follow blogs using a variety of accounts. Yet over time, we’ve seen that most people sign into Friend Connect with a Google Account. So, in an effort to streamline, in the next few weeks we’ll be making some changes that will eventually require readers to have a Google Account to sign into Friend Connect and follow blogs.
As part of this plan, starting the week of January 11, we’ll remove the ability for people with Twitter, Yahoo, Orkut or other OpenId providers to sign in to Google Friend Connect and follow blogs. At the same time, we’ll remove non-Google Account profiles so you may see a decrease in your blog follower count.
We encourage you to tell affected readers (perhaps via a blog post) that if they use a non-Google Account to follow your blog, they need to sign up for a Google Account, and re-follow your blog. With a Google Account, they’ll get blogs added to their Reading List, making it easier for them to see the latest posts and activity of the blogs they follow.
We know how important followers are to all bloggers, but we believe this change will improve the experience for both you and your readers.
Blogger support team