There's never a shortage of losers in the stock market. Let's take a closer look at five of this past week's biggest sinkers.

Company

Oct. 18

Weekly Loss

Amarin (NASDAQ:AMRN)

$2.03

60%

Select Comfort (NASDAQ:SCSS)

$18.60

29%

Molycorp (NYSE:MCP)

$5.36

24%

J.C. Penney (NYSE:JCP)

$7.00

13%

Demand Media (NYSE:DMD)

$5.20

11%

Source: Barron's.

Let's start with Amarin. The drugmaker was Nasdaq's biggest loser, shedding 60% of its value after an advisory panel shut down its attempts to expand its triglyceride-battling Vascepa. The FDA panel voted overwhelmingly against the expansion, and investors were counting on that larger patient potential to make Vascepa far more valuable.

Select Comfort was a nightmare after hosing down its guidance. This is the second time this year the company behind the Sleep Number air-chambered mattress has warned that it wouldn't be able to meet its previously issued outlook for 2013. 

Molycorp slipped after diluting shareholders with a secondary offering. Raising $225 million through offering at least 45 million shares at $5 apiece will come in handy for the rare earth minerals specialist, but it's never a good sign when you your stock closes at $7.10 while $5 is the most that underwriters are able to fetch in a secondary offering. 

J.C. Penney closed out the week by hitting yet another multi-decade low. The week kicked off with more skepticism about the fading department-store operator. An analyst discussion suggests that J.C. Penney may struggle with inventory buying power beyond this year's holiday shopping season. Speaking of which, the company also announced that it will open on Thanksgiving night.

Demand Media tumbled after Richard Rosenblatt -- the busted IPO's CEO, chairman, and co-founder -- resigned. Demand Media has struggled since going public at $17 two years ago. The market was initially excited about the prospects for the content farm's ability to populate the Web with cost-effective articles on timely concepts, but search engine algorithm changes and heightened competition slowed its growth. The stock has since shed more than two-thirds of its value.

Longtime Fool contributor Rick Munarriz and The Motley Fool have no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.