The number of Facebook members in the U.S. is about 152 million; Twitter has roughly 38 million users.
However, a new report from eMarketer reveals that Twitter’s growth is exploding in the U.S., as Facebook’s slows to single digits for the first time. Overall, the growth in membership for both sites is expected to decline over the coming years in the U.S.
According to eMarketer, Facebook membership grew by 13.4 percent in 2011 (a 25 percentage point drop from the previous year) compared with Twitter’s 31.9 percent growth (an increase of roughly 8 points from 2010). This year, Facebook users are expected to grow by 6.6 percent; Twitter’s membership will likely expand by 20.7 percent.