Twitter has been kind to a motley crew of actors, TV personalities and pop stars whose fame online outstrips that of the outside world. And it's all about getting personal.

Ashton Kutcher is the most popular user with more than 3 million Twitter followers, and LeVar Burton of Star Trek fame is more popular than pop star Lady Gaga. Cellist Zoe Keating has 200,000 more followers than mega-star Justin Timberlake.

Name recognition only takes you so far, said Jeremiah Owyang of the Altimeter Group consultants.

The social networking and blogging service that limits messages to 140 characters has a different hierarchy of who is most popular. And crowding the top are those who adopted Twitter early in its 3 1/2-year history.

Simply being a celebrity does not guarantee a following, analysts say. A loyal following, said Owyang, involves creating a dialogue with users that is personal, not self-promoting.

If they talk about Christmas, or what they're doing this weekend, said Owyang, then a conversation is begun.

Kutcher is followed closely in popularity by Ellen DeGeneres and Britney Spears.

Unlikely stars like LeVar Burton or MC Hammer participate actively in Twitter and interact with users, said Rohit Bhargava, senior vice president at Ogilvy.

These celebrities seem to genuinely care about Twitter, Bhargava said, rather than just a celebrity trying out the latest fad their assistant or PR person tells them about.

That credibility is huge when it comes to who to follow.

There is also an age factor.

Twitter has been pretty much ignored by users under 25, according to a Nielsen study, which affects popularity.

It could also explain why Oprah Winfrey is so popular even though she doesn't update her Twitter account that often. said Mark Evans of Sysomos, a media analytics firm.

Many celebrities benefited from joining early, and doing so with fanfare. Kutcher did that, then created enough momentum to stay on top, said Pete Cashmore who runs the blog Mashable.

If Kutcher joined Twitter today, he said, you wouldn't hear about it.

Twitter had nearly 21 million unique visitors last month according to comScore and, according to eMarketer, has over 18 million members, though the majority does not post actively. It is the third largest social networking site in the United States, after Facebook and MySpace.