The reasons behind Google Plus's growth have to do with Google's effort to build a connecting layer across all its services, including search, YouTube, maps and other products.
Google said last December that 500 million people had created Google Plus accounts. However, only 135 million were actively posting to Google Plus pages. Millions more were using some of the service's features, such as clicking the "+1" button.
Facebook is the leader in social media with 701 million active users, according to the report.
GlobalWebIndex's latest figures show that Twitter is growing at a slightly fastclip, increasing from 206 million users at the end of June last year to about 297 million today.