Research In Motion plunged the most in 11 weeks after saying revenue missed its forecast last quarter amid accelerating market-share losses for BlackBerry smartphones and PlayBook tablets to Apple.

Third-quarter revenue was “slightly lower” than the $5.3 billion to $5.6 billion the company had projected and earnings were “at the low to midpoint” of its forecast, according to an unscheduled statement from Waterloo, Ontario-based RIM yesterday. RIM said it doesn’t expect to meet its full-year profit target.

The shortfall — the fourth straight quarter sales missed analysts’ estimates —- puts more pressure on co-Chief Executive Officers Jim Balsillie and Mike Lazaridis as they seek to revive a company that once dominated the US smartphone market.

RIM’s market-share decline has prompted investors such as Jaguar Financial Corp. to call for a change in leadership and for RIM to divide into separate companies or seek a sale.

“The next question from a management perspective is, do they need someone different? They cannot keep going on the same course forever,” said Bahl & Gaynor Investment Counsel’s Matt McCormick, whose firm oversees $4.1 billion. McCormick, speaking from Cincinnati, said he’s “glad” his firm doesn’t own RIM stock.

RIM fell 9.7 percent to $16.77 yesterday. The stock has lost 71 percent this year.