NEW YORK (AP) — Shares of J.C. Penney Co. plunged nearly 20 percent a day after the department-store chain reported its fourth straight massive quarterly loss.

On Thursday, Penney shares fell about 19 percent, or $3.98, to $17.18. Adding that decline, the company's shares have lost 60 percent of their value since early last year.

The stock drop, which could be the one of the company's worst ever, is the latest sign that CEO Ron Johnson's plan to turnaround the retailer is failing on Main Street and Wall Street. The strategy, which Johnson started early last year, includes the company ditching coupons and most sales in favor of everyday low prices, bringing in hipper designers like Besty Johnson and remaking outdated stores.

But the company's quarterly and full-year results, which it reported Wednesday after the markets closed, reveal just how much the company is struggling with the plan.

During the fourth quarter that ended Feb. 2, Penney's revenue at stores opened at least a year — a figure the retail industry uses to measure of a store's health — dropped 31.7 percent. That's on top of hefty drops in the previous three quarters of 26.1 percent in the third, 21.7 percent in the second and 19 percent in the first. And it's steeper than the decline of 26.1 percent Wall Street had expected.

The company, which is based in Plano, Texas, widened its quarterly loss to $552 million, or $2.51 per share, for the three-month period ended on Feb. 2, up from a loss of $87 million, or 41 cents per share a year ago. Revenue fell 24.8 percent to $12.98 billion.

Penney's results for the full year were even worse. For the fiscal year, Penney lost $985 million, or $4.49 per share, compared with a loss of $152 million, or 70 cents per share, in the year ended January 28, 2012. And the company's revenue fell nearly a quarter, or 24.8 percent, to $12.98 billion from the previous year's $17.26 billion.

"It's the worst performance I have ever seen by a company in one year," said Walter Loeb, an independent retail consultant, said of the earnings report.

While acknowledging that Penney made some mistakes during a conference call with investors, Johnson said on Wednesday that Penney would start offering sales in stores every week — about 100 of the 600 or so the chain offered each year prior to the turnaround plan.

That's in addition to the sales events that the company said last month that it would start offering during holidays and other key sales periods throughout the year.

"Experience is making mistakes and learning from them, and I have learned a lot," Johnson said. "We worked really hard and tried many things to help the customer understand that she could shop any time on her terms. But we learned she prefers a sale. At times, she loves a coupon."