Shamara, the midday DJ at WUSL-FM (98.9), Power 99, is on a roll. It's 11 a.m., and she's playing "Unthinkable" by Alicia Keys and Drake.

As she plays hits for her listeners, she's also tweeting - sending Twitter messages to fans and friends on her BlackBerry.

"On air @Power99Philly come get a musical orgasm," she writes, with a link to a website where her show can be heard. "hope u gotta :) on ur face," she tweets. "Hold up I believe my friends on facebook gonna start cussing me out - ain't been there in a minute . . . brb yo."

Music, tweet music.

Shamara is, according to the website Twitaholic.com, the 19th-biggest Twitter user in the Philadelphia region, with more than 7,500 followers. Since joining Twitter 17 months ago, she has sent out an astounding 44,668 tweets, about 85 a day.

Like many users of Twitter, and like all of Philly's biggest tweeters, Shamara uses Twitter for three purposes, which melt into one another:

Promoting themselves.

Making friends, one by one.

Building communities of people who come together over shared interests.

Shamara and other huge tweeters show how, in the social-media world of Twitter, Facebook, and LinkedIn, the private is increasingly merging with the public.

It's estimated that more than 100 million people worldwide use Twitter, sending out text messages of 140 characters or fewer. Popular as a personal means of staying in touch, tweeting has also taken off in business and entertainment.

Twitter figures are rough. When users create a Twitter account, they can fill in their location - but they don't have to, and they don't have to tell the truth. Websites such as twitter.grader.com and Twitaholic count those who enter Philadelphia and track how busy they are.

Philadelphia tweets more than cities many times its size. The world's 53d-most-populous city, Philly is 24th in Twitter traffic, according to twitter.grader.com. It ranks ahead of Mumbai and Tehran and just behind Bangalore.

The top tweeters

So who are Philadelphia's top tweeters? In terms of followers, according to Twitaholic, the city's Twitter king is Ahmir Thompson, better known as ?uestlove, drummer for the Roots, the popular hip-hop band and house band for Late Night With Jimmy Fallon. ?uestlove has a remarkable 1,341,925 followers.

"Twitter is the fastest, most rapid means of communicating with my network," ?uestlove says via e-mail. "Highly effective in conducting focus groups and the Roots' demographic. . . . I can also test my comedy material and cause instant backlash in 140 characters or less."

No. 2 is Urban Outfitters, the clothing company, with 210,865 followers. The rest of the top 10, in order: Jim MacMillan, former Philadelphia Daily News photographer and now freelance journalist, 79,309 followers; John Gruber, a tech commentator who writes about Apple products on his blog, "Daring Fireball," 75,346; Bob Garrett, a social-media consultant and blogger, 73,406; a jeweler named Judy, with 30,951 followers; poet Jack Storm, whose tweets link to his YouTube channel, 25,225; marketer Beth Harte of Serengeti Communications, with 20,171 followers; life coach Phyllis Mufson, 18,613; and the Philadelphia Museum of Art, with 17,265 followers.

Hip-hop artists, poets, jewelers, bloggers - they may seem miscellaneous, except that these people are doing, on a huge scale, what millions are doing around the world. Old distinctions - between high and low, famous and not, friend and business contact - melt away on this ephemeral, on-the-go, instantaneous chat stream. Every person interviewed for this article stressed that Twitter is a great leveler. That has made it popular and powerful.

The new triangulators

Colleen Padilla, 34, known as "Classy Mommy," has a website by that name. And a blog. And a Twitter account. The website is sort of a Consumer Reports on children's clothes, toys, books, and stuff. Her blog bolsters the website, giving Padilla's take on issues. And her Twitter account - classymommy, No. 30 in the Philadelphia area (4,991 followers) - has attracted a community of mothers who turn cyberspace into a big kitchen where they can sit around and learn about life while the kettle steams.