Based on figures released by GlobalWebIndex it would appear that Google+ has become the 2nd largest social media platform, topped only by the might of Facebook.
Summary information claims "active users" (defined as “Used or contributed to in the past month”) grew 27% to 343m users in December 2012. Facebook, for the same period, had an active user count of 693m; significantly less than the number 1bn often quoted by Facebook themselves.
GlobalWebIndex, who claim to be "the world’s largest and most detailed market research on multi-platform internet usage", also noted the fastest growing network was Twitter which grew 40% to 288m.
Looking at the graph it is interesting to note that Tumblr and Pinterest both have very small market share, yet the phrase Ghost Town is so often thrown around for Google+
If you also consider that YouTube (number three in the graph) is owned by Google, it is evident the combined strength is one to match Facebook.
The full GlobalWebIndex Social Platforms update report makes for interesting reading.