Unless you've received the most recent Google Maps update, with all of the fun new integrated location sharing features baked right in, you're kind of screwed right now. Instead of waiting until the Maps update was totally pushed out to every Android user, Google flipped the switch and killed location sharing on Google+ for just about everyone.
That means you have no Google-based location sharing option until the Maps update finishes rolling out, because staged rollouts are awful.
Updating an app for the entirety of Android is hard. There are a lot of us in the world, and to make that download available to everyone at the same time is expensive in several ways. What's worse, if you send out an update and there's a bug discovered out in the wild that you didn't know about, you have to send the update all over again once you fix it.
Google's solution allows anyone to only send out updates to a small percentage of users at first, and slowly increasing that release group until it reaches 100%. It's not only a good way to make sure you don't make your entire userbase angry if something is broken, it's significantly less expensive to deliver those updates over a longer period of time.
It's entirely likely this update will finish rolling out by this evening.
But miscommunications like this are the natural consequence of this behavior. I know several people in my immediate social circle with the Maps update already. In fact, my Dad emailed me this morning with a link to add me to his location sharing group on Maps. Because I don't have the update yet, if I click that link I get redirected to a Maps support page telling me to update the app. Which, obviously, I can't do yet because the app hasn't been fully rolled out top everyone yet.
So if you lost location sharing on G+ and don't have the Maps update yet, the official answer from Google is to be patient. It's entirely likely this update will finish rolling out by this evening. But that's never going to be where this stops for some people. Just like when Pokemon Go wasn't available and people started sideloading dangerous versions of the APK that were available on some random shady website, this is the perfect opportunity for someone to tap that "Install from Unknown Sources" checkbox and leave it unchecked just so they can have this new update.
That's bad for everyone, and Google not only can but should do better.