Google+ has signed up 13% of U.S. adults so far and could hit 22%, in a year, passing Twitter and LinkedIn as the number two social media network, according to a new study.

The report, based on a Bloomberg and YouGov poll of 1,003 U.S. adults from July 29 to August 2, revealed that 71% percent of U.S. adults use Facebook, but that number will drop to 69% a year from now. Among people who use both services, 30% say they plan to cut the time they spend on Facebook. However, 31% of Google+ users say they've abandoned their Google+ accounts or never posted anything on them.

Twitter and LinkedIn will continue to grow, however.

Twitter is set to add 3% of the U.S. population over the next year for a total of 20% of the U.S. population. LinkedIn, which is expected to add 2%, will also hit 20%. Meanwhile, 45% of respondents who signed up for Google+ said they read content on the site every day. For Facebook, the figure was 62%. For Twitter it was 42% and for LinkedIn, 8%.