(Reuters) - Shares of Herbalife (HLF.N) plunged again Friday, feeling the brunt of heavy selling in a week where prominent short-seller Bill Ackman called the company a "pyramid scheme."
The stock closed 19 percent down at $27.27, its lowest in nearly two years.
The selling continues a bad run for the stock, which has been hit hard in recent days as Ackman said he was shorting the stock, giving a three-hour presentation Thursday where he called the weight management company's model unsustainable.
Pershing Square Capital Management said on Friday it had launched a website that provides information about the company, including source data that was used in the presentation.
Shares have fallen 36 percent in the last three days and have lost nearly two-thirds of their value since hitting a life-high in April.
Ackman, known for agitating for management change at companies his fund invests in, has targeted Herbalife via one of his biggest short positions in years.
Ackman said he had been building his short position in the company's stock for several months and that he was so sure of his position that he believed the company's stock price would eventually go to zero.
More than 42.2 million Herbalife shares had changed hands on Friday, far surpassing the 2.8 million shares traded on average over the past 50 days.
Similar stocks in the space were also down. Nu Skin Enterprises Inc (NUS.N), a skin products company, closed 14 percent lower at $34.51. Blyth Inc BTH.N, which sells nutritional supplements through its ViSalus unit, closed down 8 percent at $14.75.
Herbalife said on Friday it would hold an analyst day in the week of January 7 to respond to Ackman's claims.
Option volume on Herbalife hit an all-time high on Friday, a day that also marks the expiration of December equity options. Herbalife traders exchanged 136,000 puts and 85,000 calls, or 11 times the combined daily average, according to options analytics firm Trade Alert.
Out of that volume, 41 percent were December contracts that expire after market close. The most popular contracts are the December $27.50 strike put followed by the May $22.50 strike put.
Reporting By David Gaffen, Doris Frankel and Maria Ajit Thomas; Editing by M.D. Golan and Saumyadeb Chakrabarty