WASHINGTON (AFP) — Struggling US newspaper publishers are painfully aware of it but a survey released on Friday found that the use of online classified advertisement sites such as Craigslist is soaring.

The number of Web-connected US adults who use online classified sites has more than doubled in the past four years, according to the survey by the Pew Research Center?s Internet and American Life Project.

Forty-five percent of Internet users surveyed said they have used online classified sites, compared with 22 percent of online adults who had done so in 2005, Pew said.

It said that on any given day, nine percent of US Internet users visit online classified sites, up from four percent in 2005.

Pew said its findings "highlight the growing importance of such sites to Internet users and reflect the changes in the audience for classified ads -- both those who place them and those who make purchases."