By ANNE D’INNOCENZIO

Associated Press

J.C. Penney is the biggest loser.

Shares of J.C. Penney Co. plunged nearly 16 percent on Thursday, the biggest loser on the Standard &Poor’s 500 index for most of the day. The drop comes a day after the department-store chain reported its fourth consecutive larger-than-expected quarterly loss on another steep sales decline

The drop means that Penney shares, which are now trading at around $18, have lost nearly 60 percent of their value since January of last year when CEO Ron Johnson announced his plan to ditch hundreds of sales in favor of everything low prices. At the time, investors had sent Penney shares up 24 percent to $43 as a vote of confidence

The stock drop is the latest sign that Johnson’s turnaround strategy is failing on both Main Street and Wall Street. The company’s quarterly and full-year results, which it reported Wednesday after the markets closed, revealed that shoppers still aren’t buying it. But the sell-off shows that investors, too, are concerned that the plan won’t work.

“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, a New York based independent consultant.

Penney’s spokeswoman Daphne Avila declined to comment on Thursday’s stock movement. But Johnson on Wednesday acknowledged to investors that the 1,100-store chain had made some mistakes. He also told them that Penney would start offering sales in stores every week.

“Experience is making mistakes and learning from them,” Johnson told investors on Wednesday. “I have learned a lot.”

If J.C. Penney’s results are any indication, Johnson is right. Penney reported on Wednesday after the markets closed that it widened its quarterly loss to $552 million, or $2.51 per share. Revenue fell 24.8 percent to $12.98 billion.

Revenue at stores opened a least a year dropped 31.7 percent. The measure is a key indicator of a retailer’s health. Customer traffic dropped 17 percent in the quarter, worse than the 10 percent drop in the third quarter.