After raising a $75 million investment at a $1 billion valuation earlier this year, Mercari announced it has seen more than 20 million app downloads in the U.S. The company started a North American hiring binge earlier this year and is aiming to double its staff in the U.S over the next 12 months. Mercari’s ultimate goal is to take on eBay and Craigslist on their home turf — and beyond.