Half of America Is Using Social Networks By SOMINI SENGUPTA

Social networks have crossed another milestone.

For the first time, half of all adults in the United States said they use a social networking site, according to a survey released Friday by the Pew Research Center.

That’s 50 percent of all Americans, not just those who say they are online. Six years ago, when Pew first conducted a similar survey, only 5 percent of all adults said they used social sites, like Facebook, LinkedIn or MySpace.

It is a sign of how deeply and widely social networking companies have penetrated the lives of ordinary people and in turn, transformed the ways in which people communicate, authorities govern and companies sell things.

Parents use Facebook to vet nannies, car makers to launch new models, police to keep tabs on suspects. Federal government authorities are preparing this weekend to use social networking sites for hurricane preparation on the East Coast.

The Pew survey found that among adults who are online the rates of participation are higher: 65 percent, according to the survey, up slightly from 61 percent last year.

Not surprisingly, the sites are more popular among younger people: 83 percent of people surveyed in the 18-29 age bracket said they use social networking sites, compared to 51 percent of those in the 50-64 age bracket. The young are also twice as likely to use social sites every day.

The survey by the Pew Center’s Internet and American Life Project described women aged 18-29 as “the power users” of social sites, with 89 percent of them using social networking sites and 69 percent using them every day. Such a stark finding has obvious implications for advertising on sites like Facebook.

Neither income nor education seemed to have any statistically significant bearing on the use of networking sites. A separate study published by the Pew Center in June found that black Americans continue to be more likely to be on Twitter than whites: One in four African-American users of the Internet said they use Twitter “occasionally,” and 11 percent said they used it daily. Twitter penetration still lags considerably: 13 percent of those online describe themselves as Twitter users and the lion’s share of them use it on their smartphones.

The Internet is still more commonly used everyday for e-mail and search: 61 percent said they went online every day to check e-mail, 59 percent for search and 43 percent for social networking.

There are some signs that social networking is reaching its limit. Asked for one word to describe their social networking experience, the most common was “good.” However, one in five respondents sounded less upbeat: they used words like “boring,” “time-consuming” and “overrated” to describe their experience.