For several months now, it’s been fair to describe Twitter as the hottest startup in the tech sector, but a new study from online metrics firm comScore suggests that the microblogging site may be cooling off.
The key data point in comScore’s analysis is the monthly tally of U.S. visitors to Twitter.com. In September, comScore registered 20.9 million unique visitors to the site, a negligible increase of less than one half of 1 percent from the previous month.
More striking, the August traffic count actually marked a decline from July, when Twitter hit a high-water mark of 21.2 million unique visitors, according to comScore.
In contrast, Facebook has continued to distance itself from the social networking pack, adding nearly 3.3 million unique U.S. visitors in September for a total of 95.5 million.
Since September of 2008, Twitter has seen its U.S. unique visitor count soar more than 1,700 percent, according to comScore.
Of course, any measure of Twitter traffic is thrown off by the myriad third-party sites and applications that have sprung up enabling users to access the service without visiting Twitter.com. Services like HootSuite, TwitPic and TweetDeck make it difficult to arrive at a reliable picture of just how large Twitter is, and how quickly it is growing.
A comScore spokeswoman told InternetNews.com that the firm does not track usage of Twitter on third-party sites and apps.
Twitter did not immediately respond to a request for comment on the numbers.
In May, research firm Nielsen Online took a stab at analyzing off-site Twitter traffic. The researchers were following up on a report in which they’d suggested that many users who create a Twitter account quickly lose interest and abandon the site. Critics pounced on the survey for failing to account for third-party sites and apps.
In its follow-up, Nielsen cast a wider net and looked at 30 off-site tools for accessing Twitter, in addition to its data on Twitter.com. The researchers said that their original findings held, affirming its original “Twitter quitter” analysis.
comScore’s analysis of global traffic to social networking sites is due out later this month.