NEW YORK (TheStreet) -- TrueCar (TRUE) - Get Report  participated in the sale of more than 600,000 new cars in 2014, said the company's founder and CEO Scott Painter. That represents about 4% of last year's entire 16.5 million-unit new car market.

In December, TrueCar saw 5 million unique visitors to its automotive pricing and information Web site, either through or one of its hundreds of partners, which include AAA and American Express  (AXP) - Get Report . That represents 80% year-over-year growth, Painter told TheStreet TV at the North American International Auto Show in Detroit.

At the show, TrueCar unveiled a new app targeting Millennials. The app allows users to have interactive conversations throughout the car-buying process.

Painter called it a new direction for TrueCar and the future of car buying and selling.

"We believe Millennial buyers are ready to use their phone in an entirely new way," he said. "Buying a car is an inherently mobile activity and therefore they need 'their friend' in the car business, TrueCar, with them from the point of purchase and all the way through the transaction."

TrueCar finished its first year as a public company up about 160% after opening on the Nasdaq at about $9 a share. Painter sees a large market that remains to be tapped.

After being boycotted by car dealers in 2012, TrueCar now has one out of every three dealers in the U.S. on its platform, or about 10,000 car dealerships. Dealers spend up to $10 billion each year on advertising and incentives. Automakers' budgets are seven to 10 times that much. 

TrueCar allows dealers and car makers to promote their products on its Web site, so it benefits from that spending.

Shares of the Santa Monica, Calif.-based company were down 4.7% on Wednesday, to $20.10.