Mike Swift / San Jose Mercury News

AUSTIN, Texas — Matthew Rosenberg, co-founder of a startup on the leading edge of the hottest technology trend at this year’s South by Southwest Interactive festival, looked around at the throngs in the Texas streets outside the influential tech conference and shook his head in wonder.

“We’re the new rock stars,” said the 28-year-old co-founder of New York-based Fast Society, a mobile service that allows groups of people to communicate simultaneously through a text-message-based system. “Entrepreneurs are the new rock stars.”

Fast Society is one of a long list of startups at SXSW Interactive competing to use text messaging as the basis for group sharing of locations, photos, voice, text and other social information.

The 17-year-old fast-growing interactive conference was the place where Twitter first came to prominence in 2007. It was the place in 2009 where the concept of smart phone location check-in services was first popularized by the New York startup Foursquare.

SXSW remains one of the most fashionable places to seek out the emerging trends in personal technology, particularly on the mobile and social web. Still, even some young entrepreneurs worry that the mushrooming event is losing its soul, as corporations and what Rosenberg called “the beautiful people” are drawn by the money and cultural interest behind the boom in online social media.

Among the other hot startups and trends making their debuts at SXSW Interactive for 2011: digital music services where your tunes are stored on the Internet “cloud,” instead of your phone or computer, and next-generation search engines like Moodfish, which uses terms like “sunny,” “sensual,” “intense” and “quirky” to find appropriate entertainment nearby.

And there was actress Demi Moore’s favorite SXSW startup: Zaarly, where you send out an offer from your smart phone to pay a fee to have a service performed, and people in your geographic vicinity can respond to your offer.

Moore and husband Ashton Kutcher, who have become active investors in tech startups, are among the backers of Zaarly. Both, along with talk-show host Conan O’Brien and other Hollywood notables — SXSW also includes a film festival — showed up at a sweaty, broom-closet-sized studio in downtown Austin. They all talked about the intersection of social media and entertainment on Facebook Live, the live talk show that streams over the Web.

After discussing how massive support on Twitter and Facebook helped show O’Brien that he needed to keep performing after losing his spot on “The Tonight Show,” the talk-show veteran bantered with interviewer Randi Zuckerberg, sister of Facebook CEO Mark Zuckerberg, about the public obsession with the iPad 2.

“Right now, someone at Apple is watching: ‘He displeases us,’ ” O’Brien joked to Randi Zuckerberg in a comically menacing voice. “ ‘Destroy the one they call Conan.’ ”

For now, Rosenberg and the other three members of Fast Society aren’t making rock star money. Younger entrepreneurs like Rosenberg are mainly interesting in building companies around smart phone applications, as mass-market social networks like Facebook and Twitter, once the shiny new baubles of SXSW, now need to be augmented by social services that are more personal and flexible.

In the words of Jared Hecht, the 24-year-old co-founder of competing service GroupMe, the new services are like a “reply all” button for texting, or a mobile chat room for you and your closest friends. Big social media platforms have become so large and homogenous “that the communication there often becomes sterile,” Hecht said. “People are feeling, ‘I need something that is a little more me.’ ”