An upgrade from Piper Jaffray Cos. sent Groupon shares flying on Monday. The firm upgraded the stock from neutral to overweight. The pop was the most the online marketplace has seen in the last three months. Piper Jaffray has upgraded its recommendation for Groupon, citing the company’s narrowed focus and marketing spending as driving growth. … Continue reading “Groupon (GRPN) Shares Are Exploding”