All of that being said, Google+ still has a great deal to offer writers in the form of communities. There are dozens of active writing communities on Google+, spanning everything from poetry, to self-publishing, to blogging.
I've listed below the communities I have found most useful as a writer, but there are many more. You can find a full list of all communities here: https://plus.google.com/u/0/discover
General
Writers, Authors, Bloggers - 57,365 members. Public community. "This is a community for writers, authors, publishers, bloggers to share ideas, thoughts, suggestions. Also post links to your website to build followers & advertise your products."
The Writers Community - 52,995 members. Public community. "Any and all things concerning writing and writers."
Writers' Corner - 44, 108 members. Public community. "Love to write stories, poems and all things? Join the realm of Blissful Writers who enjoy writing poems, stories, novels, quotes of inspiration. novellas and so forth. We have both the traditionalists and self-publishers. Categories such as Romance, Poetry, Haiku, Inspiration, Sci-Fi, Horror, Erotica, Fantasy, Thriller, Mystery, Crime and more."
Writing - 32, 621 members. Public community. "The art and science of writing." Links to blog posts and upcoming books are allowed.
Writers' Blogs - 29,376 members. Public community. "Share you writer's blog here. Share any blog on the topic of writing or reading. Authors and writers, share your social media links."
The Art of Writing - 18, 356 members. Public community. "A place for Writers of all genres to share, inspire, advise and share ideas about writing better. Ask for people to critique, make contacts for agent referrals and to just have fun doing what you love."
Writers of Google+ - 11,536 members. Public community. "A gathering of all the writerly Google plussers!"
Where Writers and Authors Meet - 8,678 members. Public community. "Where fellow writers and authors can meet other writers and authors. Readers are welcome to come on in and talk with us too ;) Feel free to share book free days, reviews, tours, guest posts, or anything else of note. Written something online? Drop a link for us to look into! Have some promotional, publishing, or writing advice to share? Feel free! Is anyone out there 'just' a blogger? Come on in! We can all learn from each other's experiences! There is a lot of good writing out there that has yet to be discovered."
Genres
Fantasy Writers - 14,448 members. Public community.
Horror/Mystery Writers - 1,928 members. Public community.
Poets of G+ - 23,258 members. Public community.
Poetry - 53,943 members. Public community.
Romance Writers and Readers - 5,714 members. Public community.
Science Fiction - 89, 821 members. Public community.
Science Fiction Writers - 5,906 members. Public community.
Short Stories and Poems - 6,857 members. Public community.
Speculative Fiction Writers - 5,583 members. Public community.
Young Adult Books - 8358 members. Public community.
Young Adult Lit and Writing - 44,330 members. Public community.
Book Promotion and Marketing
Promote Your Book! - 18, 154 members. Public community.
Writers' Market, Tools, Tips, Showcase and Support - 9,583 members. Public community.
Discussing Book Marketing & Promotion - 9,421 members. Public community.
Authors - Blatant Promo 4 Writers, Blogs! - 8,343 members. Public community.
Author Marketing Club - 4,437 members. Public community.
APE - 3,526 members. Private community.
Readers
Reading - 25,256 members. Public community.
Readers and Writers - 9,448 members. Public community.
Reviewers
Book Reviews - 20, 736 members. Public community.
Book Reviewers - 18,955 members. Public community.
Blogging
Blogging - 66,336 members. Public community.
Bloggers Network - 28,399 members. Public community.
Blog Writers United - 2,644 members. Public community.
Self-Published Authors and Self-Publishing
E-Book Publishing - 23,293 members. Public community.
Indie Readers and Writers - 14,341 members. Public community.
Indie Authors and Readers - 10,760 members. Public community.
Kindle and Ebook Writers - 9,208 members. Public community.
Self-Publishing and Book Marketing - 7,846 members. Public community.
Self-Publishing Children's Books - 575 members. Public community.