Why one investor believes Pinterest is worth $2.5 billion

When Facebook tanked in its initial public offering, the social network eroded the perceived value of private consumer Internet companies -- save for Pinterest. Despite a lack of revenue, the scrapbooking site is now worth an unfathomable $2.5 billion.

Making an educated guess at best, investors like Rick Heitzmann, founder and managing director of FirstMark Capital, have pinned their pocketbooks to a service that merely offers the promise of future reward. FirstMark Capital was Pinterest's first institutional investor. The firm has participated in every one of the startup's funding rounds, including the monster $100 million round announced yesterday.

"Pinterest is a company whose product has really hit a core consumer use case," Heitzmann told CNET. "It's one of the fastest growing sites in the history of the Internet."

That use case, said Heitzmann, is discovery -- or a way to start your online quest for a new backpack, first-date dress, or vegan meal to cook for dinner.

Heitzmann is, at the very least, right about one thing. Launched in 2010, Pinterest is the most modern example of a consumer Internet sensation. The site, which is dominated by women who seek inspiration around fashion, food, home, and travel, unofficially reaches around 45 million people monthly in the U.S., according to Quantcast. Officially, Pinterest doesn't publicly talk about its massive member base.

When asked about how Pinterest will make money, Heitzmann expectedly ducked the question, indicating nothing beyond the obvious: that Chief Executive Ben Silbermann and the team are thinking about revenue.

"Discovery is a core tenet of the Internet," he said, "and being at that point where people are discovering things is important."

Pinterest can be the jumping-off point for whatever whim or fantasy captures your imagination. Just as you would flip through a Better Homes and Gardens magazine for inspiration, you can skim over friends' pins and dream about your next kitchen remodel. For many women, Pinterest replaces the fashion magazine as a more satisfying way to find, collect, and gab about all the dresses and shoes they desperately want to add to their real-life collections.

The aspirational elements of the site are intermixed with more realistic shopping occasions. Take, for instance, my friend's male co-worker who was desperately searching for a pair of earrings his wife had pinned to one of her boards. The husband knew that his wife really wanted the celadon gems, and so he asked my friend to help him find a place to buy them. The search proved futile, but solve situations like that and Pinterest is sitting on a goldmine.

Purchase intent is absolutely present on Pinterest, as Heitzmann pointed out with his own anecdote about looking for a backpack to buy. In other instances, say planning for a home remodel, Pinterest drives intent, which puts the startup in the promising position of being able to understand intent -- for advertisers' benefit, perhaps? Heitzmann wouldn't say directly.

Even still, it doesn't sound as if Pinterest intends to turn on any revenue-making features in the immediate future. The company, the repeat investor said, will continue to focus on product and delighting its audience.

So what, then, makes Pinterest worth $2.5 billion right now? The answer is as hard to pin to down as the company's actual value.

Pinterest, said Heitzmann, has already accomplished the foundational element of all great companies: It's created a product that millions of consumers around the world love.