Meet ZocDoc, now NYC's richest start-up

ZocDoc is the new king of New York start-ups.

The company, which lets patients book medical appointments online and from mobile devices, raised more than $150 million, increasing its valuation to about $1.5 billion, based on a recent filing with the state of Delaware, where ZocDoc is incorporated.

That puts ZocDoc ahead of MongoDB, a big data company that raised money at a valuation of around $1.2 billion in October, and makes it New York's highest-priced start-up, according to data from research firm CB Insights.

Money is flooding into emerging Internet and mobile services, with hedge funds, private equity firms and mutual funds investing in private technology companies at an unprecedented rate and software start-ups raising more cash than at any time since the dot-com bubble.

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Even as New York can trumpet recent successes like Tumblr's $1.1 billion sale to Yahoo and Buddy Media's acquisition by, the metro area is far behind the Silicon Valley in terms of attracting capital. Of the $9.5 billion that venture capitalists invested in the U.S. in the first quarter, almost half went to Silicon Valley while New York companies received only 10 percent, according to the National Venture Capital Association.

ZocDoc skates the line between two red-hot industries: online marketplaces and business software. Individuals can book appointments for free and at the last minute with dermatologists, dentists and chiropractors. More than 5 million people in over 2,000 U.S. cities use the service every month, according to ZocDoc's website.

Benefits of booking with ZocDoc

For about $3,000 a year, medical professionals can promote their services and manage their schedules, making slots immediately available after cancellations. Just as Airbnb lets homeowners rent out spare bedrooms and Uber helps limousine drivers find passengers, ZocDoc enables doctors to keep the office full, but not too full. Airbnb and Uber, both based in San Francisco, are worth $10 billion and $17 billion, respectively.

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Founded in 2007, ZocDoc had previously raised close to $100 million, with DST Global and Goldman Sachs leading the last round, a $75 million pool in 2011.

According to the latest disclosure from the end of May, ZocDoc sold 5.41 million Series D shares for $28.22 a piece, totaling $151.2 million. The previous round, Series C, was price at $14.57 a share, valuing the company at about $700 million. The filing does not say who led the round, and a representative declined to comment.

—By CNBC's Ari Levy