If U.S. consumers are using a broadband Internet connection they’re probably on Facebook, according to a new survey by Netpop Research LLC called “Social Animals 2011.”

The report found that Facebook is the most-visited social site, with 73% of U.S. broadband consumers using the social media giant.

YouTube, at 49%, came in second. The remaining sites on the top 10, in order, are Craigslist at 34%, MySpace at 17%, Groups.Yahoo.com at 14%, Twitter at 14%, Groupon at 13%, LinkedIn at 9%, Classmates.com at 8% and Groups.Google.com at 6%.

According to the Netpop survey of 1,253 U.S. broadband Internet users, 73% contribute content online. 39% post content on a social networking site, 38% upload photos, 27% rate or review products, 13% upload videos, 12% update their location, 12% post content on a blog or forum, and 10% post content on a mircoblog such as Twitter. Compared with a Netpop survey in 2009, microblogging has grown 400% and posting to a blog or forum is down 25%.

The age of consumers who contribute content to the social web skews young. 82% of 18- to 34-year-olds and 77% of 13- to 17-year-olds contribute; that number drops to 67% for age 35 and up. And women contribute more content than men: 78% of women and 66% of men go social.

“Social media is on the rise in the U.S. as Americans engage in a larger variety of online social activities,” says Cate Riegner, vice president of brand insights and cofounder of Netpop Research. “One in four broadband users now engage in at least four social media activities on a regular basis. Most anyone over the age of 35 is baffled by all the tweets, tags and uploads; but ask a GenYer the last time they checked their e-mail and you’ll receive a disinterested shrug. Indeed, between Facebook and YouTube, the most popular social media brands, and Twitter, the dominant microblog brand, we see where media is heading in the 21st century.”