If at first you don't succeed...

Four years ago, Robin Thicke was a hippie-haired pop producer trying to jump - start his own singing career.

He had survived boot camp in the radio world, having penned tracks for artists such as Christina Aguilera and Mya . He had recorded an album -- "A Beautiful World" -- which mixed rock, funk, R&B, and pop and boasted a radio-friendly single, "When I Get You Alone," an intense dance tune that sampled Walter Murphy's "A Fifth of Beethoven."

The young singer, who happens to be the son of "Growing Pains" dad Alan Thicke , even had a good stage name -- he had shortened his moniker to the one-word "Thicke."

Thicke was about to be the next big thing.

But then he wasn't.

"I'm not R&B enough for R&B radio. I'm not hip-hop enough for hip-hop. I'm not rock enough for rock radio. Therein lies the wonderful struggle," says Thicke, who opens for John Legend at Avalon tomorrow.

Radio- friendly or not, "When I Get You Alone" never found a home on the airwaves. Locally, hip-hop station JAM'N 94.5 played the tune for a short time, but it fell off the rotation. Back then, with his shoulder-length hair and scruffy beard, Thicke was all wrong. He sounded like he wanted to be the next Stevie Wonder or Marvin Gaye, but he looked like a Phish fan.

Plus, there was the matter of another young man with a similar sound, an ex-boy-band crooner named Justin Timberlake who had just released his own first album, "Justified." Even though multiple publications including The New York Times used Thicke and Timberlake as examples of blue-eyed soul going big, only one of the artists became a mega-star. Thicke fell off the map.

"The funny thing is, I'd been hearing [stuff] like that since I was 16," Thicke says of predictions in 2002 that he was on the verge of fame. "People had always been saying that -- and then nothing."

Now, the build-up and letdown may be happening again.

Thicke, now 29, released "The Evolution of Robin Thicke" last month with a moderate amount of fanfare. He now bills himself with his full name and has cut off his locks for a look that resembles Timberlake or George Michael in his heyday.

Thicke made the new disc more appealing to a mainstream audience by adding stars from the world of rap and R&B, such as Lil' Wayne and Faith Evans . For this album, Thicke was picked up by the Star Trak label run by the Neptunes, the production duo responsible for much of what's on hit radio, from Gwen Stefani to Snoop Dogg.

Thicke's website opens with a flashing quote from the Neptunes' Pharrell Williams : "Robin Thicke is going to change music."

Another promise. And still, you've probably never heard of him.

The first single from "Evolution" -- "Wanna Love U Girl" -- features vocals by Williams, whose cameos, like producer Timbaland's , have become a good- luck charm for pop tracks. But the Thicke song, which was released shortly before the album, has yet to find regular rotation on Boston stations.

Though a few of Thicke's new singles have become fan favorites on MTV for a short time (his song "Shooter" with Lil' Wayne had a brief run on "Total Request Live"), "radio doesn't love me," Thicke says. Even in today's fragmented radio market, mainstream airtime is still necessary to get pop-star huge.

Rob Walker, who runs Star Trak with Williams, says it may take time.

"Robin has created amazing music," Walker says, via e-mail. " And we think his music has great impact. . . . Everyone will catch up. . . . It will happen."

Locally, Newbury Comics on Newbury Street says it sells one or two copies of the disc a day. Best Buy says it doesn't even carry it.

Alden Fertig, operations manager for Emerson College's WERS-FM (88.9), says underperformance by any pop-star-in-the-making with a big label behind him is somewhat puzzling. After all, backing by a personality like Williams and a big label can be more important than talent.

But according to Fertig, Thicke can't blame Timberlake for his lack of commercial success, even though both of Thicke's albums were released on the heels of Timberlake discs, which prompted comparisons by critics of the artists' wardrobes and falsettos. (The All Music Guide has described Thicke as "Timberlake for the skeptical set.")

Fertig says if anything, the Timberlake comparisons should help . Oftentimes, similar acts unintentionally work in tandem, especially fringe artists, Fertig says. Gnarl s Barkley , for instance, may have OutKast to thank for its own radio play.

"It was getting played on hip-hop stations, pop stations, rock stations, alternative stations," Fertig says of the Gnarl s Barkley song "Crazy." "It really crossed over. If something tests well, stations are going to play it. And the copycats."

What may be stalling Thicke's arrival is that when he first came on to the scene, he was, for whatever reason, given the narrow label of "soul," a genre that has gone largely unrecognized by mainstream radio, according to Fertig. WERS plays two of Thicke's singles during a show on weekend nights called "The Secret Spot," which airs neo-soul singers such as Legend and Jill Scott who don't get much airtime otherwise.

It's not bad company to be in, Fertig says, and Thicke agrees, saying he's proud to have spent his fall opening for Legend and India.Arie.

But for Thicke, whose discs are supposed to have pop potential, it's still frustrating. He wouldn't mind actually becoming the next big thing one of these days.

"When I was 7 years old, I didn't say 'I want to have average success commercially,' " Thicke says. "My favorite artists were Michael Jackson and Prince. Of course, I want to be beloved and to have panties [thrown at me]. But I guess if you get 1,000 panties thrown at you by fans and you love what you're doing and you're making people feel good . . . it may not be 10,000 panties, but it's a start."

Meredith Goldstein can be reached at mgoldstein@globe.com.