(Reuters) - Facebook Inc's shares slid 6.2 percent to another record low on Tuesday, diving for the third straight day since lackluster results showed decelerating user growth and revived doubts about its ability to sustain its rich valuation.

A sobering report from Bernstein Research, combined with online chatter about the potential proliferation of automated Facebook accounts and a looming sell-off of employee shares next month all conspired to rock the stock, analysts say.

Facebook has lost more than 40 percent of its value since becoming on May 18 the first American company to debut with a value of more than $100 billion.