5 of Last Week's Biggest Losers

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.

Source: Barron's.

Let's start with K12, the online educator offering Web-based curriculums for students from kindergarten through high school. The company lost more than a third of its value after offering disappointing enrollment trends, and its guidance was also a bombshell, with a new revenue range that's well short of where the pros were perched. The effectiveness of K12's platform has been called into question in the past, though it's hard to ignore the cost-effectiveness of the virtual classroom. However, now sluggish enrollments are holding K12 back.

Amarin took its biggest hit on Friday, after the FDA issued a review that questions the effectiveness of Amarin's fish oil-based triglyceride-lowering drug, Vascepa. Fish oil in general has come under fire as a treatment for people trying to lower their triglyceride levels.

Liquidity Services was flowing the wrong way after a weak report of September sales volume. The company's gross sales volume of $77.7 million last month was 10% below last year's showing. The report reverses positive gross sales in previous months.

Jamba, the parent of Jamba Juice, got squeezed after hosing down its guidance. The company was originally expecting same-store sales growth of 4% to 6% for all of 2013, but now it's targeting flattish results after a disappointing summer quarter. Jamba blames weak retailing trends and uncooperative weather in key markets, as Jamba's smoothies are at their most desirable during hot summers.

Finally, Celldex Therapeutics took a hit after Jim Cramer talked down the biotech and many of its high-flying peers on Mad Money. 

"After having some incredible runs this year, I think it's time to ring the register on pretty much any biotech that's smaller than $10 billion," he argued. "The same goes for all of the other small-cap biotechs that are up huge for the year."

He called out Celldex by name, fitting the bill on both fronts, as the $2.2 billion company has more than quadrupled this year. 

"I still adore these small-cap biotech companies, but I hate greed," he concluded. "If you don't ring the register on their stocks here, you are being a bad little piggy."