Zynga planning secondary offering: report Tue Mar 13, 2012 4:39pm EDT (Reuters) - Zynga Inc, the video game company that went public in December, is planning to sell additional shares in a secondary public offering, Bloomberg reported on Tuesday. The newswire, citing two sources, said the offering would let investors sell shares, and large stockholders may also agree to a longer "lock-up" period. A "lock-up" period during an IPO means that certain investors with a large number of shares are usually not able to sell their stock until a pre-arranged date. One source told Bloomberg that Zynga wants to avoid what happened with LinkedIn Corp, whose shares fell following the end of its lock-up period last fall. A Zynga spokesman declined to comment on Tuesday. Zynga shares fell 2.8 percent to close at $13.38 on the Nasdaq. Reporting By Liana B. Baker; Editing by Gary Hill