The percentage of US millionaires using Facebook in 2011 has nearly doubled to 46 percent from 26 percent last year, according to wealth consultancy Spectrem Group.

Similarly, 47 percent of ultra high net worth investors, those with a net worth of $5 million to $25 million, and 55 percent of the mass affluent, who have a net worth of $100,000 to $1 million, are also using Facebook.

Blogs rank as another good way to reach the wealthiest Americans, Spectrem found. Nearly one-third (30 percent) of UHNW investors say they either read or would read blogs by trusted financial advisers. The percentage is 20 percent for millionaire...