Plotkin, who managed one of the firm's biggest portfolios, has been in talks with SAC founder Steven Cohen about his desire to start a new fund for some time, the sources told CNBC on Thursday.
Cohen will invest more than $200 million in Plotkin's new venture, The Wall Street Journal reported Thursday.
JPMorgan hedge fund unit Highbridge Capital Management recently hired two portfolio managers from the firm to manage money for its stock trading funds, according to The New York Times.
SAC had about 1,000 employees before it began to shrink due to a combination of layoffs, office closings and traders departing, according to the Times report. The hedge fund now employs about 850.
-CNBC's Kate Kelly contributed to this report.