NEW YORK — J.C. Penney Co. was the biggest loser Thursday. Its shares plunged nearly 17 percent to $17.57, the largest decline on the Standard & Poor’s 500 index, a day after the department-store chain posted its fourth consecutive quarterly loss — one that was larger than expected.
The shares have lost about 60 percent since January 2012, when chief executive Ron Johnson unveiled a plan to ditch hundreds of sales in favor of everyday low prices. Thursday’s fall is the latest sign Johnson’s strategy may fail. ‘‘I fear it will be much worse, as consumers continue to walk away from J.C. Penney and its financial health continues to deteriorate,’’ said Walter Loeb, an independent consultant in New York.