From Chicago Business, powered by Crain’s By: Steve Hendershot February 27, 2012 Tech entrepreneur-turned-investor Shawn Riegsecker understands the value of an angel investor firsthand because his own company relied on one. That was in 2005, when Mr. Riegsecker’s Centro LLC was looking to develop its technology platform. (Chicago-based Centro helps ad agencies purchase digital display advertising.) Mr. Riegsecker had used his own money and credit to build the business to that point but then raised $1.8 million from 20 angels, mostly based in Texas and New York.