Facebook Inc. was cut to a sell rating from neutral by BTIG LLC, which cited the social- networking company’s struggles to generate revenue from its mobile users.

Facebook risks annoying its mobile customers by cluttering the service with advertising, creating a “growing tension between the Facebook user experience and monetization,” said Richard Greenfield, an analyst at BTIG in New York. He lowered his 2012 revenue forecast to $4.9 billion from $5 billion and the 2013 projection to $5.6 billion from $5.9 billion.

“We have grown increasingly concerned with Facebook’s mobile monetization approach,” Greenfield said in a report.

Facebook fell as much as 3.3 percent in early trading in New York. The shares have fallen 45 percent since the company’s initial public offering in May.