According to Geekwire, the new financing round is led by private-equity firm Warburg Pincus. OfferUp declined to comment on its valuation, but it has long been rumored to be the Seattle area's only unicorn, a startup valued at more than $1 billion.

The company connects buyers and sellers looking to unload or purchase everything from sewing machines to sofa beds using a mobile-friendly marketplace.

Founded in 2011, OfferUp was started by Nick Huzar and co-founder Arean Van Veelen after they struggled to find ways to unload household items that had accumulated in their homes. Since then OfferUp's free Android and iOS app has grown well beyond Seattle. It is available in every major city across the U.S. and ranks No. 42 overall in the iTunes store, above other free apps from brand names like Yelp, eBay and Lyft.

OfferUp recently brought in Peter Wilson, site director for Google's expanding Kirkland campus, to be vice president of engineering. Wilson will help scale the engineering team at OfferUp, which is on pace to process more than $14 billion worth of transactions this year and just won App of the Year at this year's GeekWire Awards. For context, eBay's gross merchandise volume was $15 billion eight years after its launch -- this growth was highlighted by Mary Meeker in her annual 'Internet Trends' report earlier this summer.