PASADENA, Calif. -- When Paula Abdul wanted to make a splash, she didn't call a press conference or give an interview. She used Twitter, the same social media site where last month she told her fans, "Craving some ice cream ... Mmmm."

Insipid as some posts to Twitter -- called "tweets" -- may be, the site is a well-used communications tool by public figures. On Aug. 4, Ms. Abdul used Twitter to announce in multiple tweets -- each one limited to 140 characters -- that, "With sadness in my heart, I've decided not to return to ['American Idol']."

Even as some media corporations seek to limit how much their employees participate in social media sites -- Disney-owned ESPN sent guidelines to its employees this month instructing them to get permission from a supervisor before engaging in any form of social-networking and to bear in mind they are representing ESPN -- celebrities continue to tweet away.

On Aug. 7, Derek Hough, one of the dancers on ABC's "Dancing with the Stars," announced he and girlfriend Shannon Elizabeth had broken up, with each of them posting the news to Twitter. A week ago, comedian Kathy Griffin used the site to declare to her 156,000 Twitter followers, "There's a new love in my life ... ." The tweet linked to a photo of Ms. Griffin arm-in-arm with Levi Johnston, father of former Alaska Gov. Sarah Palin's grandson.

"It's easy and it's only 140 characters, which I think is essential when dealing with stupid celebrities," Ms. Griffin said of Twitter at a NBC-Universal party here on Aug. 5. "You should not give them pages and pages of a blog. You should limit them."

Ms. Griffin said she does her own tweeting, but some celebs pass that work along to their assistants who serve as ghost twitterers. Other celebs don't tweet at all but imposters do it for them.

Matt Damon, Paul Walker and Dennis Hopper all said earlier this month that they don't use Twitter, but imposters have set up accounts in their names, complete with the stars' photos.

To prevent impersonation of famous figures, Twitter is experimenting with a "Verified Account" feature that uses a white check mark inside a blue emblem atop the person's profile. The absence of the badge does not mean an account is fake.

"I'm not on any of those," Mr. Damon said. "I'm actually so busy and I'm out of touch with a lot of people I want to be in touch with. My wife did it recently and she was so inundated she kind of ran out of time."

Mr. Hopper said it was weird to think about someone impersonating him online.

"I don't know that much about the Internet," he said. "I've tried to avoid it. Jack [Nicholson] and I decided a long time ago that since we couldn't type, we might as well stop so we didn't really go on with it."

Athletes have also started using Twitter to the extent that some NFL teams, concerned about what might be expressed in a tweet, have set guidelines or even asked players not to participate. The Steelers have no official Twitter policy, said team spokesman Dave Lockett.

Twitter isn't just an outlet for actors, athletes and other public figures. Fictional characters have taken to it, too.

Actor Nathan Fillion, star of ABC's "Castle," offers witty tweets ("Dear Diary, I hope we win an Emmy. I would have it made into a necklace and wear it until it pulled out my back") and so does his alter-ego, mystery novelist Richard Castle. Late last month ABC set up a Twitter account for the character (as WriteRCastle) as a way to promote the series and an upcoming book "authored" by Castle. Already the fictional character has 7,900 followers.

Kassia Krozser, editor/owner of the Web site Booksquare.com, said each social media site has its own character. Facebook is a place to connect with people you already know, but Twitter is more akin to a cocktail party with conversations you eavesdrop on.

For celebrities, Ms. Krozser said Twitter allows them to engage in conversation with fans while marketing -- but it can't be just about the hard sell.

"If you're out there talking to [a lot of fans], you're building your name," she said.

The celebrities-on-Twitter trend picked up steam earlier this year when Ashton Kutcher raced CNN to see which of them could be the first to garner a million "followers" on their accounts. Mr. Kutcher won and has now passed the 3 million followers mark.

"I originally got on to follow five people in the tech industry I was interested in," Mr. Kutcher said earlier this month. April's race-to-one-million against CNN was a way to garner media attention for the charity Malaria No More and World Malaria Day on April 25.

"Anytime someone takes on the media, it becomes a media story because the media loves to write about the media," Mr. Kutcher said.

Actor David Blue, a recurring guest star on "Ugly Betty" who's a lead on fall's "Stargate Universe," said he joined Twitter a year ago to stay in touch with fans. Since then, he's encouraged fellow actors, including "Stargate" co-star and former Pittsburgher Ming-Na, to begin tweeting.

"[Actor/director] Jon Favreau and I were speaking at an Entertainment Weekly party at Comic-Con, and he said it allows you to dispel rumors that might be out there and gives [fans] a true peek at what's going on without having to worry about it having to get filtered through anyone else's mouth," Mr. Blue said. "It's also dangerous because of that."

And that's the rub: For celebrities or politicians (think: Sarah Palin), Twitter tweets or Facebook status updates cut out the middleman -- those pesky journalists -- but it can also be a personal publicist's nightmare if a client tweets something controversial.

Ms. Krozser pointed to the example of novelist Alice Hoffman, who in late June took a reviewer to task in a series of tweets that damaged her own reputation in the process. Ms. Hoffman no longer appears to have a Twitter account.

For some in the public eye, use of Twitter began as a personal communications tool and grew into something more. Shonda Rhimes, executive producer of "Grey's Anatomy" and "Private Practice," said she didn't intend to tweet much herself and after fans started to find her on Twitter, she initially stopped tweeting. Then she decided to use her account to promote her shows.

"It's a way to communicate with the fans, a way of letting them know stuff," Ms. Rhimes said. She posted a link to a photo from the set of "Practice" star Taye Diggs when the show resumed production this summer.

Jane Espenson, a writer on "Buffy the Vampire Slayer" and "Battlestar Galactica" who's head writer on the upcoming Syfy series "Caprica," got on Twitter after she exhausted screenwriting advice for her blog, janeespenson.com.

"This seemed like a way I could give small amounts of script-writing advice or updates from the writer's room or personal observations without the necessity of crafting a whole blog post," she said. "I was also coming at it from the other side. I had people I was fans of who I wanted to hear what they had to say."

Ms. Espenson follows producer/director Paul Feig ("The Office") and comic actors Eddie Izzard and Stephen Fry.

Of course, not all Twitter accounts are built to stand the test of time (or TV ratings). Actress Jenna Elfman ("Dharma & Greg") stars in the fall CBS comedy "Accidentally on Purpose" and she incorporated the show title into her Twitter name, JennaOnPurpose.

"I thought it would be a fun way to put my own voice out there and promote the show, too," she said. And if the sitcom fails as 80 percent of new TV programs do, what becomes of her Twitter account name?

"I guess I'll take one thing at a time."