A look at growth rates for both Facebook and Twitter in the US reveals that while Facebook’s growth continues to slow, Twitter’s will remain in the double digits through 2014.

Facebook’s growth was at 38.6% back in 2010, but lowered significantly to 13.4% in 2011 as growth finally began to plateau.  This year, Facebook’s growth rate will drop to 6.6%, and is projected to go as low as 3.6% by 2014.

Twitter, with a much smaller user base and more room to grow, will see much higher growth rates over the next few years.  According to eMarketer’s forecast, Twitter’s growth peaked in 2011 at 31.9% (an increase from 23.5% in 2010). Now numbers will slowly begin to decline, with only 20.7% growth in 2012 — still more than three times Facebook’s projected growth this year. By 2014, Twitter’s growth rate is projected to drop to 14%.

These growth rates will see Twitter’s U.S. user base nearly double between 2010 and 2014, according to eMarketer projections.  By 2014, Twitter will have 37.6 million users (compared to Facebook’s expected 150 million.)

eMarketer’s estimates are based on an analysis of survey and traffic data from research firms and regulatory agencies; company releases; historical trends; internet and mobile adoption trends; and demographic and socio-economic factors.