Payment network Dwolla has grabbed another $16.5 million in funding. The company announced that the Series C round was led by Andreessen Horowitz and included previous investors Village Ventures, Thrive Capital, and Union Square Ventures.  

"We've designed a powerful payments engine that unlocks a safer, more affordable, and, ultimately, a more compatible way to move money in today's economy," said Dwolla founder and CEO Ben Milne. "While this investment validates how far we've come and what we've achieved, this is about finding the right people in the right places to build the best possible products for our users."

Dwolla will use the new funds to support its enterprise pipeline, and to open a fifth office in San Francisco, the company said. Currently it has offices in Omaha, Neb., Kansas City, Mo., New York and its headquarters in Des Moines, Iowa. The San Francisco office will open in June and will be led by the company's COO, Charise Flynn.

According to Dwolla, the user base for its flat-fee platform has grown 15 percent month-over-month and its annual processing volume is now in the billions.

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