At midmorning in New York, Amarin shares were down 19 percent to $9.70, after earlier dipping to $9.40 in the biggest intraday drop since August 2011. The Dublin-based company’s shares had gained 56 percent in the 12 months through Thursday.

Investors had expected Amarin to sell itself or find a partner to market Vascepa, the company’s treatment for severely high levels of triglycerides, said Akiva Felt, an analyst for Wedbush Securities in San Francisco. Instead, the company announced Thursday that it raised $100 million and started hiring a sales force for the medicine. The financing from Pharmakon Advisors and the start of a sales force may mean no sale is on horizon, he said.

“The concern is that this may be a signal that a deal isn’t imminent,” Felt said in a telephone interview Thursday. “There had been expectations that there would be a strategic agreement in the near term.”