* Goldman, Morgan expected to lead IPO -source
* IPO seen in second half -source
* JPMorgan expected to land co-manager role -WSJ (Changes sourcing; adds detail that values are still in flux)
NEW YORK, April 14 (Reuters) - Groupon is likely to pick Goldman Sachs (GS.N) and Morgan Stanley (MS.N) to lead a second-half initial public offering that could value the fast-growing daily deals site at $15 billion to $20 billion, a source familiar with the matter said on Thursday.
Groupon could raise as much as $1 billion in the IPO, which could come in the second half of 2011, although the exact size had not yet been determined, said the source, who was not authorized to speak to the media.
The source cautioned that the size of the IPO and the market value of the company were not final and could change.
The possible market value was first reported by the Wall Street Journal, which also said that JPMorgan Chase & Co (JPM.N) was expected to have a co-manager role.
Groupon was not immediately available for comment.
The multibillion-dollar valuation is the latest in a string of high valuations for hot Internet companies including Facebook and Twitter, and raises questions about how these companies, albeit fast-growing, could ever justify the sky-high valuations.
Groupon said it has been profitable since June 2009, but does not disclose financial information.
Groupon Chief Executive Andrew Mason told Reuters in January it was talking to bankers about an IPO.
The site, which offers daily discounted deals at local restaurants and retail outlets, turned down a $6 billion buyout offer from Google Inc (GOOG.O) in December. (Reporting by Clare Baldwin; Additional reporting by Paritosh Bansal and Martinne Geller; Editing by Gary Hill)