If you can't have Mark Cuban as an investor in your startup, it still pays to count him as a customer.

Three-year-old menswear brand Mizzen+Main is building an impressive list of celebrities who are trading their starched cotton dress shirts for the company's stretch-knit button-downs, and famous clients like Cuban and Daymond John seem to be helping the company grow sales. Although it's worth noting that the Dallas-based company shares a local fan base with Cuban, who owns the Dallas Mavericks basketball team.

In addition to the two Shark Tank hosts, Mizzen+Main has customers in NFL quarterbacks Drew Brees and Joe Flacco, best-selling author Tim Ferriss, and actor Chris Klein, all of whom have shared photos of themselves wearing the brand on social media. The genius behind its marketing is this stealth strategy: It monitors sports stars and other celebrities on Instagram for photos in which they happen to be wearing its shirts and reposts them to the company’s account.

Mizzen+Main has also attracted high-profile investors. These include Astor & Black founder David Schottenstein, who led a $1.2 million in Series A investment in the company in August 2014. The business sells 80 percent of its product online and has wholesale distribution in between 70 and 80 retailers, including Saks Fifth Avenue. The company has 11 full-time employees.

The buzz is translating into sales. While 29-year-old founder Kevin Lavelle declined to disclose Mizzen+Main's annual revenue, he says the company hit "seven figures" in 2014, and has already matched last year's sales in just the first six months of 2015. The company also reached profitability in March and May. "We weren't profitable in April because we sold out of product," Lavelle says.

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What's so special about the shirts?

Mizzen+Main uses moisture-wicking, wrinkle-free synthetic fabric that companies like Nike and Under Armour use for athletic apparel. The soft, flimsy material isn't typically used for shirts with stiff collars and cuffs, but once Lavelle figured out a way to make the material hold up a tie and look indistinguishable from traditional dress shirts, the brand was born.

So how did Mizzen+Main land Cuban as a customer?

"His wife got him a whole bunch of shirts for Christmas last year, and he's got a bunch more now," Lavelle says, adding that the company has clients in between 150 and 200 professional athletes who enjoy being able to wear the same comfortable fabric they use for workouts as formal attire. The name Mizzen+Main refers to the first two masts of a sailboat. "It’s an homage to the classic East Coast lifestyle and traditional menswear," Lavelle says.

While having Cuban share photos of himself wearing the shirts on social media has been good for business, Lavelle says it feels a little strange benefiting from the Shark Tank host's Instagram activity.

"I've never actually spoken to Mark," he says.