NEW YORK ( -- The popularity of YouTube is growing at an astronomical rate, as web traffic to the video-sharing site grew 75% just in the week ending July 16, from 7.3 million to 12.8 million unique visitors, according to Nielsen/NetRatings. Traffic to the site has grown nearly threefold -- 297% -- since January, making it the fastest-growing site online.

Still without an ad model, YouTube is signing sponsorships as its web traffic soars.
Still without an ad model, YouTube is signing sponsorships as its web traffic soars.

Page views soar
The number of web pages viewed on the site has grown at an even faster pace, increasing 515%, from 11.8 million in January to 72.4 million in June, Nielsen finds. The average time spent at the site has increased 64% during the same period, from just more than 17 minutes to nearly 28 minutes.

In about a year and a half, founders Chad Hurley and Steve Chen have watched YouTube go from a video-sharing site for their friends to the most-visited video service online, attracting more than 20 million U.S. users in May -- compared with 11.1 million for Microsoft's MSN Video. The two have become the envy of every media company from New York to Los Angeles, as evinced by Mr. Hurley's belle-of-the-ball status at last month's elite Allen & Co. media summit in Sun Valley, Idaho.

Still building an ad model
Still in the process of building its advertising model and sales team, YouTube is experimenting with a number of sponsor partnerships. Last month, NBC struck a deal with YouTube to promote its fall TV lineup just months after ordering the site to take down copyrighted video. Under the terms of the agreement, NBC is creating an official NBC Channel on YouTube to house its fall preview with exclusive clips to promote shows such as "The Office." And earlier this month, Walt Disney tapped YouTube to promote "Pirates of the Caribbean: Dead Man's Chest," with rich-media banner ads.

Men are 20% more likely to visit YouTube than women, with unique audience composition indexes of 113 and 88, respectively, according to Nielsen/NetRatings. Visitors between 12 to 17 years old index the highest among the various age groups, at 142. They are nearly 1.5 times more likely than the average web user to go to YouTube.