J.C. Penney Co. chief executive officer Ron Johnson is facing mounting pressure after the first year of his turnaround plan resulted in the department-store company’s lowest annual sales in more than two decades.

The shares dropped the most in nine months after J.C. Penney said its net loss in the quarter ended Feb. 2 widened to $552 million, or $2.51 a share, from $87 million, or 41 cents, a year earlier. The Plano, Texas-based retailer’s annual revenue slid 25 percent to about $13 billion, the lowest since at least 1987.