The best replacement for google plus is facebook.

The best alternatives to google plus are rated as following:
★★★★★  facebook
★★★  flickr
★★★  picasa
★★  twitter
★★  google drive
★★  google places
★★  facebook users
★  google
★  linkedin
★  google groups
  facebook which is better
  places

Your alternative for google plus is not listed? Suggest!
Speaking about google plus, one probably shouldn't forget about youtube.

Other search terms related to google plus and their ratings are:
★★★★★ youtube
★★★★★ gmail
★★ picnik
★ twitter
account
You have in mind a companion for google plus and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of google plus in all years. Click on graph for more.
google plus
facebook
flickr