The average number of monthly visitors to U.S. newspaper websites increased nearly a third in the first half of 2006, underscoring the importance of the web to papers buffeted by falling circulation and ad revenue.

The average number of unique visitors to online newspaper sites in the first half was more than 55.5 million a month, according to a study released by the Newspaper Association of America (NAA), reports Reuters. That compares with 42.2 million a year earlier. The number of pageviews at newspaper sites increased 52 percent in the first half.

Importantly, newspaper websites are attracting younger readers. Newspaper websites helped drive a 15 percent increase in total newspaper audience for 25-34-year-olds, and a 10-percent increase for 18-24-year-olds.

NAA also launched a new interactive tool, built by Scarborough Research, designed to allow advertisers to generate their own reports on national and local newspaper print and online audience data (large PDF), comparing selected markets or newspapers across a range of demographic segments. The tool is available on a new NAA advertiser site.