Facebook Inc. (FB), operator of the world’s largest social-network, declined after a report from Capstone Investments said the number of users fell over the past six months.

The shares (FB) of Menlo Park, California-based Facebook decreased 0.6 percent to $28.09 at the close in New York, adding to a 8.1 percent slide yesterday. Shares of Zynga Inc. (ZNGA), which gets most of its revenue from games played on Facebook, dropped 5.2 percent to $4.58.

U.S. users decreased 1.1 percent over the past six months, Rory Maher, an analyst at Capstone, said in a report today. Of 23 countries where Facebook had at least 50 percent market penetration, growth was little changed or down in 14 nations over the past three months, he said.

“This could be an issue for Facebook growth since we estimate that outside of Southeast Asia and some countries in Latin America, most markets are approaching 50 percent penetration,” Maher said in the report.

To contact the reporter on this story: Lisa Rapaport in New York at lrapaport1@bloomberg.net

To contact the editor responsible for this story: Tom Giles at tgiles5@bloomberg.net