One in five US consumers age six and older (20%)—roughly 56.8 million people—say they have played a game on a social networking website in the previous three months, according to a report from The NPD Group.

Among social gamers—those who play games on at least one social networking site—35% say they are new to gaming, having never participated in any other type of gaming before they started playing on social networks.

Though women and older age groups are more likely to be new gamers, a large number of men (47%) are still playing social games.

Still, despite such popularity, few users are willing to pay for social games: Just 10% of social gamers say they have spent money on social games, and only 11% say they are likely to do so in the future.

The findings are discouraging for traditional game developers and publishers. Social network games are affecting spending on other types of gaming activities: Social gamers report spending 20% less on gaming overall since they started playing social network games.

"There are many distinctions between the players who spend money and those that don’t," said Anita Frazier, industry analyst at The NPD Group. "While social network gaming has caught on with a mass market audience, it's not without its challenges. Players are frustrated by slow loading and performance issues and report getting bored by the games easily. Clearly, these types of games will have to continue to evolve if they hope to hold their audiences and incentivize them to spend money playing."

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Such social gaming adoption levels are roughly in line with separate research from PopCap Games in January 2010, which found that roughly 24% of US and UK consumers regularly played games on social networking sites, such as Facebook and MySpace.

Women were found to constitute 55% of social gamers, according to PopCap Games. Only 6% of gamers were age 21 or younger, and 58% were over age 40.

About the data: The NPD study is comprised of two surveys: 1) NPD's Games Acquisition Monitor, fielded April 5-20, 2010 among a nationally representative sample of 2,008 US social network gamers age 6+; and 2) A pre-identified portion among social network gamers age 6+, fielded June 1-9, 2010 via an online survey to NPD's Consumer Panel. Social gamers are defined as those who are members of or users of at least one social network site and who also currently play games on at least one social networking site. Also included in this report is data based on 935 individuals who do not play social network games, but who use social sites.