From a long-term sustainability perspective, there will come a time when it makes sense for him to expand to an older and more diverse demographic. And that begins with showing he can get a following among tween boys. Furthermore, the tween girl market is a crowded field, while on the other hand, retailers are consistently clamoring for something to serve the boys’ market, where there’s a lot of white space.

With Justin Bieber’s fan base largely consisting of tween girls, does it pose a challenge for him in terms of where he can license the Bieber brand? History is filled with stories of child stars that never got beyond a niche appeal, so the concern is a valid one. However, Bieber does seem to be doing a good job of expanding.

His Super Bowl commercial with Ozzy Osbourne was well received and his Saturday Night Live and MTV Music Award vignettes were fun and showed the kind of attitude advertisers appreciate. But, because his fan base is mostly female at the moment, it makes sense for his licensing deals to target this group. And so far that seems to be the approach the brand is taking.

For example, his nail polish has been wildly popular since its December launch, he has just launched Someday, a perfume, and I would expect that other traditional “pop sensation” licensing deals such as bedding, posters, trading cards and dolls will also be a great success. (It would be terrific if someone figured out how to trademark his haircut, including its more cropped update. It seems like every high school teenager is sporting the Bieber hairstyle. At least they aren’t asking their barber for the Pauly D!)

I would imagine apparel and accessories are right around the corner for Bieber. There are many unisex products through which he can target both male and female fans, like sunglasses, sneakers, watches and hats. I can see a line of Justin Bieber-branded Wayfarers, perhaps in collaboration with Ray Ban.

Boys’ apparel would require somewhat of a transformation, á la Justin Timberlake, who was in a famous boy band in 1998 and didn’t have a clothing line until 2005, which was launched under the William Rast brand, not his own name. As for how he could make that transformation, he’d do well to follow the other Justin — Timberlake that is —who has laid out a pretty good road map. NSYNC wasn’t outrageously popular with male teenagers, but his William Rast clothing line seems to be doing quite well with both sexes.

Bieber needs to stay relevant – which he shouldn’t have a problem with – and showcase his talents in other arenas. Acting roles in Alpha Dog and The Social Network have broadened Timberlake’s fan base significantly. It looks as if Bieber is taking the same approach with his pursuit of acting gigs, CSI in particular. He has proven that he has box office appeal—grossing over $30 million in the opening weekend of his biographical film Never Say Never—so it is only a matter of time before Hollywood producers come knocking for feature films. He’ll have to pass on the obvious “teen heartthrob roles” and continue to pursue edgier roles in order to eventually broaden his appeal.

However, a word of caution — maintaining popularity and relevance in the media will be much easier than maintaining relevance in consumer products. The retail shelves are littered with the remnants of very famous celebrities (who are still very famous), but who no longer resonate with consumers. There’s always a fresh crop of celebrities waiting in the wings.