Hearst and Pulitzer. Murdoch and Turner. Dunham and Jeter?

More and more, the fastest-growing and buzziest media startups are springing not from traditional publishers and broadcasters but from the minds of celebrities with recognizable names but minimal industry experience. The past week has brought ample fresh evidence of the trend.

First, Time Inc. acquired Hello Giggles, a website co-founded by quirky actor Zooey Deschanel, for a reported $30 million. Then, on Tuesday, Lena Dunham, the writer/director/star of HBO's "Girls," made a deal to partner her nascent e-newsletter, Lenny, with Hearst Corporation. On the same morning, The Players Tribune, a sports-news website launched by retired New York Yankee Derek Jeter, announced that it had secured $15 million in new funding, with Kobe Bryant participating in the round.

Celebrities leveraging their fame to launch media properties isn't a new phenomenon, of course. Martha Stewart, Oprah Winfrey and Dr. Oz are among those who have started magazines bearing their names.

But the new breed of celebrity media entrepreneurs are different. They're less interested in cashing in on their personal brands than in building new ones. They don't even have the kind of brands that seem obviously leverage-able. Winfrey reached 30 million viewers a day at the height of her fame; the average audience for "Girls" is well under 1 million. Dunham and Deschanel are both internet obsessions, but that's as much because of their haters as their fans. The same goes for Gwyneth Patrow, now a would-be lifestyle doyenne thanks to her Goop newsletter, and Ashton Kutcher, proprietor of a happy-news website called A Plus. Jeter may be the unlikeliest media mogul of all: During his playing days, his main interest in journalism was in avoiding being the subject of it.

Why are so many celebrities seeking, and finding, success in the media business now? Three key reasons:

1. Low cost of production. Digital tools make it radically cheap to produce, edit and distribute content in all its forms, including video and audio (ie. podcasts). That means celebrities whose appeal is more niche than mass can publish at an artisanal scale commensurate with the size of their followings.

2. Social media. One of the biggest hurdles to becoming a publisher is answering the question: What would I say? Most actors and athletes don't blog, but most of them are on Instagram, Facebook and Twitter. Maintaining their social followings has helped celebrities think of themselves as content producers, not just performers.

3. The decline of legacy media brands. Celebrities have a symbiotic relationship with news outlets: In exchange for promotion of their projects, they endure interviews and photo shoots. But most of the celebrity-oriented magazines and websites they used to count on for promotion have dwindled in reach and impact with the waning and fragmentation of traditional media. That has changed the cost/benefit math on working with them while also creating opportunities for competing with them.