Google+ app is a very popular social app for Android. After various bugs fixes now the Google+ app updated with Chromecast support. It allows you to cast the Google+ stream to Chromecast device.
The Chromecast will show a similar mirror of your feed as your device shows. Google will soon roll this update to all devices, before that if you want try install app on your device from below given link. The APK is signed by Google and upgrades your existing app. You can download the latest Google+ version 4.5 APK from below given link.
File name: com.google.android.apps.plus-18.104.22.168928916.apk