ERIN CONROYNEW YORK (AP) ¿ The pipeline of initial public offerings for 2010 looks promising as private equity firms look to cash in on their investments after coming back to the nearly defunct market in the fall. Online networking companies may take center stage. So far, the company generating the most buzz hasn't even filed for an IPO: social networking site Facebook, which has many betting its creation of a dual-class stock structure in November is a precursor to going public. IPO market trackers say other popular online networking companies could soon offer shares to the public. Micro-blogging site Twitter and business networking site LinkedIn will likely follow if Facebook is well received. Restaurant review site Yelp and Internet telephone service Skype, which was sold by eBay Inc. to a group of private investors in November, could also join the line. "Once Facebook makes that move, it will literally be pandemonium," said Scott Sweet, senior managing partner at IPO research firm IPO Boutique. "It will clear the way for everyone else." As recently as six months ago, there was little excitement in the IPO market after it dried up as the economy worsened. But a flurry of debuts came in the second half of 2009 as confidence in stock markets grew. In the last year, companies raised about $100 billion globally, and $22 billion in the U.S., through initial public offerings of common stock. The amount raised in the U.S. is about equal to the 2008 total, but that year, the majority of the money came from the $18 billion offering of credit card processor Visa Inc. Both years combined still don't add up to the $59.7 billion collected in 2007.