Rebecca Minkoff made waves in the fashion world in 2005 when an oversize handbag she designed, cheekily named the Morning After Bag, became the must-have bag among those young women who might just find themselves staying out until sunrise. Figuring out how to stay relevant to those customers as they have gotten older has been the challenge facing Minkoff and her brother Uri, co-founders of a New York City-based fashion line named after Rebecca. With $35.7 million in revenue in 2011 and a three-year growth rate of 498 percent, Rebecca Minkoff earned the No. 706 spot on the 2012 Inc. 5000. Below, Rebecca and Uri explain how staying connected with their customer base has helped them remain ahead of the curve. --as told to Judith Ohikuare

Uri: Our customer when we first started was someone just like Rebecca. She was 25 at the time, and she became the company's model and muse. She had a particular style that people loved. As she moved into her 30s, we started to notice that women have such important first experiences between 20 and 30 where fashion really comes into play: the college graduation and first serious job; the first serious dating experience and then getting engaged; and after that marriage and children. We became a brand that is geared toward women between 20 and 35 who want items that look good and have a luxury feel, but not a luxury sticker price.

Rebecca: The task of a designer is to set trends. You just hope that you can find the right inspiration that allows you to do that. Thankfully, I've got really talented people surrounding me who might be looking at the newest photographer's work or at the latest in hair and makeup or new music. I also go to events like Coachella, which is happening in April.

I might find the next band I want to use for an upcoming runway show, and it's where I can see trends starting and being formed. I get to see our customer demographic in person and spend a couple of days with her. All of that can help you decide what you're going to stand for as a brand.

UM: We take a multifaceted approach when we are figuring out our product line. It's a blend of art and science. Rebecca travels a lot, so there are so many artistic influences that she's able to draw from--from music to museums. But there's also a lot of science as well.

We examine past orders in different categories to see how they've performed historically to help us forecast our future orders. Much of our success is also based on the relationships we've established with customers on social media.

Instagram is our No. 1, go-to platform in terms of engagement. We've used responses from followers to gauge customer feedback and to help us in our discussions with retailers. For example, there was a style we loved, but one national retailer wasn't interested in buying it. Until, that is, I showed them the thousands of Instagram likes it had received and the hundreds of comments from followers about how much they loved it. In the end, that customer demand was why that retailer decided to buy the product.