Chicago ? People around the world interact with Alecia Dantico all day. Usually, though, they don’t know whether she’s young or old, male or female.

What her followers on Facebook and Twitter know is that’s she’s a friendly, sometimes sassy, blue and gold tin of Garrett Popcorn. That’s the icon of the popular Chicago-based snack food that has tourists and locals lining up around the block at locations here and in New York City.

And when Dantico sends out a “virtual tin” of popcorn to a fan over Twitter, she’s breaking new ground in the way companies market themselves, joining a growing number of social media experts hired to man Twitter, Facebook and similar sites.

“My day starts on Twitter and it doesn’t really end,” Dantico says. She keeps her BlackBerry on at all hours to respond to followers in different time zones. “It’s driving my family crazy, but that’s OK.”

Multinational corporations, such as Ford Motor Co. and Coca-Cola Co., are beginning to use social media to increase positive sentiment, build customer rapport and correct misinformation, says Adam Brown, Coca-Cola’s Atlanta-based director of social media.

“Having the world’s most-recognized brand, we feel like there’s an obligation or a responsibility when people are talking about us, we have a duty to respond,” Brown says.

Dantico, who is getting a doctorate in communications with an emphasis in building brand identity in online communities, says she has seen an uptick in sales when she’s tweeted from events since joining the company in June.

She mentions popcorn in her tweets, and has helped customers secure tins for special events, but never implores followers to go out and buy some. Successful selling through social media is much more subtle.

“Social media is all about being social,” says Nora Ganim Barnes, a marketing professor and director for the Center for Marketing Research at the University of Massachusetts Dartmouth. “It’s not called selling media. The biggest mistake companies make is using social media to hawk products. It’s a turnoff.”

Large Fortune 500 companies have been the slowest to adopt social media strategies, Ganim Barnes says. But not-for-profit organizations have been the fastest.

“It’s free,” she says. “And they’ve never had such access to media before.”

Recent research by Ganim Barnes and colleagues, though, points to a rapidly growing familiarity with social media, even among the world’s biggest brands.

“It’s bigger than Twitter, MySpace, Facebook or blogs,” she says. “It’s about engaging people.”

The lightning-fast pace of social media, and Twitter in particular, has forced businesses to act in a whole new way, says Brown, of Coca-Cola. “If you don’t respond within three or four hours, you might as well not respond at all,” he says.

Scott Monty is working to create a social-media strategy for his company, Ford Motors, where he serves as digital and multimedia communications manager in Dearborn, Mich.

Whether your business is large or small, Monty advises those interested in expanding to social media to stand back and listen before diving in.

“It’s not the typical one-way push kind of conversation,” Monty says. “You wouldn’t burst into a cocktail party and just start handing your business card to people and leave. The online space is no different.”