Here's an article from Blogger Buzz: The Official Buzz from Blogger at Google on how to expand an audience with Google+.
One thing I notice is where the article says:
Kelly always shares her blog posts from her personal Google+ profile and the Miami Fashion Bloggers Google+ page, a page she contributes to with almost 400,000 followers.
And that seems to be key to this, the idea of contributing to a widely-read page on a subject that one is interested in and write about.
Here's the link: