Celebrity Brandmatch: Jay-Z, Katy and Kiefer Owe it All to Groucho and Gracie

If Amy Sedaris pitching Downy in a perky new campaign rings a bell, it's because celebrities have been sudsing up for brands since the early days of Hollywood. Think back to the golden days of radio, when Jack Benny plugged Jello in his opening line, "Jello, everybody, this is Jack Benny," and Bob Hope promoted Pepsodent toothpaste. And in the early days of television, George Burns and Gracie Allen peddled Carnation Milk, Groucho Marx touted Prom Shampoo and Ozzie and Harriett shilled for Aunt Jemima Pancake Mix. Before he was President, Ronald Reagan stumped for Chesterfield cigarettes.

In today’s world of 24/7 social media, celebrity endorsement, backing and entrepreneurship (from Gwyneth Paltrow's Goop to Jessica Alba's Honest Company) have reached new digital platforms. This week Stamped, a mobile app and website that lets people share reviews of anything they like, announced new celebrity backers including Justin Bieber, Ryan Seacrest and Ellen DeGeneres, and investments from Columbia Records, Eric Schmidt and The New York Times Company, bringing its financing to over $3 million.

“You can see Justin’s collection of favorite things,” commented Stamped co-founder Robby Stein to the New York Times. “It’s a way to check out his recommendations and also see what your friends and taste makers are into.” Social video sharing services SocialCam, Viddy and Cinemagr.am, have celebrity fans Rihanna, Shakira and Tyra Banks, respectively, working their brands and even Foursquare has hired a Hollywood agency to woo celebrity users.

Yet when a star messes up publicly, it's not just the personal brand of the celeb that takes a hit, but his or her commercial interests too — witness the scandal surrounding Kristen Stewart, whose affair with the married director of Snow White and the Huntsman has upset her Twilight beau, Twihards and current co-stars alike.

Still, brands and stars can't keep their paws off each other — just witness the latest round of hook-ups:

• Kiefer Sutherland for Axe fears no Susan Glenn
• Selena Gomez is partnering with Case-Mate on its upcoming "Right Case, Right Occasion" campaign
• Kate Hudson is returning as Ann Taylor’s face for fall 2012
• Katy Perry is stepping in as the celeb face of popchips in the wake of co-owner Ashton Kutcher's botched campaign
• Jay-Z is promoting Duracell Powermat: 

Even "serious celebs" can't resist — cue journalist Lisa Ling (below) for Nectresse Sweetener. But celebrities might lend their face, if not their heart, to marketers.

Look at Sedaris, who may have lent her perky domestic diva persona to Downy, but she'd much prefer to lend her brand to causes such as PETA, where the ardent animal rights activist has spoofed Blackglama's "What becomes a legend most?" campaign in a partnership that's closer to her heart ... but may not pay her bills.