New York - Facebook's stock is up following a disclosure that its CEO, Mark Zuckerberg, won't sell stock in the company for at least a year.Zuckerberg holds about 504 million shares and options. The company currently has about 692 million shares eligible for sale.The concern is that if Zuckerberg floods the market with additional shares, prices would go down further. He will be eligible to do so in November.The stock is still trading at less than half of the $38 that it went for in Facebook's May initial public offering. It gained 85 cents, or 4.8%, to $18.58 in morning trading Wednesday. That more than wiped out Tuesday's loss, during which the stock hit an all-time low of $17.55.Facebook revealed Zuckerberg's commitment in a regulatory filing late Tuesday. *Follow Fin24 on Twitter, Facebook and Google+.