Twitter’s growth these days seems to be coming from abroad. ComScore data shows a 6.7 percent jump from August to September in worldwide vistors to 58.4 million (which translates to 949 percent increase from a year ago). The 20.9 million visitors from the U.S., in contrast, has remained flat since June.

These numbers do not include mobile or desktop app usage. But if Twitter hopes to become the first Web service to reach one billion users, it had better speed up its growth. Facebook, which is outgrowing Twitter in the U.S. even on a percentage basis, had an estimated 411 million visitors worldwide in September (up 5.5 percent from August). And Google is at 879 million unique visitors globally, according to comScore.

Twitter’s recently announced deals to provide its full firehose of Tweets to both Bing and Google should drive more traffic from the search engines. And maybe new features aimed at making Twitter more manageable such as Twitter Lists, which is expected to be introduced to all users sometime this week, will also reignite growth.