The Twitter craze is difficult to explain, but it’s a social media phenomenon that is attracting visitors at record rates. And the buzz over this social network’s online and mobile platforms is not showing signs of slowing.

In 2008, Compete — a web analytics company — released data that suggests Twitter’s website usage (not counting mobile clients) grew by a mouth-dropping 752 percent, after it started that year with an average of only 500,000 unique monthly visitors (visitors encompass registered users and those who visited the site without signing up for active accounts). By year’s end, Twitter boasted an average 4.43 million unique monthly visitors, with more than one million in December alone. More recently, comScore — a digital marketing measurement company — reported that through June 2009 Twitter had 11.5 million active Twitter accounts and 44.5 million unique monthly visitors worldwide (up by 19 percent compared to May 2009). With 24.5 million of these unique monthly visitors residing outside the U.S., Twitter has indeed gone international.

Today, Twitter is the fastest growing social network, ranking 52 for the largest website, according to comScore data. In terms of buzz, Twitter’s mention on blogs, message boards and forums has matched Facebook, which is a platform four times the size of Twitter.

Based on these staggering statistics, Twitter seems like a sure-fire bet for your upcoming social marketing campaign. But what is the primary demographic of Twitter users, and how does this demographic coincide with your target audience? As you prepare your upcoming social marketing campaign, consider the latest study about Twitter users prepared by The Nielsen Company: “Teens Don’t Tweet.”

In July 2009, Nielsen released market study findings to clarify a June 2009 report conducted by Sysomos Inc., a social media analytics company. By analyzing a sample set from the 11.5 million official Twitter accounts, Sysomos concluded that only .7 percent of Twitter profiles disclosed a user age. Of the .7 percent, 65 percent indicated an average user age of less than 25 years old. But these numbers are based solely on registered users, so Nielsen set out to also assess those who visit Twitter’s website without signing up for service.

Relying on its NetRatings panel of 250,000 U.S. Internet users, Nielsen sampled an audience consisting of Twitter registrants and general visitors alike. Data suggests that Twitter’s growth is not being fueled by youth after all, particularly children, teens and young adults. “In June 2009, 16 percent of Twitter website users were under the age of 25. Bear in mind, persons under 25 make up nearly [one-fourth] of the active U.S. Internet universe, which means that Twitter effectively under indexes on the youth market by 36 percent.” At the same time, Nielsen’s audience measurement revealed that approximately 64 percent of Twitter users are between 25 and 54, with more than 90 percent of Tweetdeck’s audience over 25. “Furthermore, Twitter’s reach is 6.6 percent for kids, teens and young adults, [but] it is 12.1 percent for those over 25, implying that adults are trying Twitter at nearly double the rate.”