Activist investor Elliott Management is seeking to replace Twitter /zigman2/quotes/203180645/lastsale TWTR -4.24% CEO Jack Dorsey, Bloomberg News reported late Friday. The $40.2 billion hedge fund run by Paul Singer has taken a large stake in the social-media company and wants major changes, people familiar with the matter reportedly told the news outlet. Twitter declined to comment on the report when reached by MarketWatch. According to Bloomberg News, Elliott Management has nominated four directors to Twitter's board. Dorsey has been scrutinized for running two publicly traded companies simultaneously: Twitter and the payments processor Square /zigman2/quotes/205989440/lastsale SQ -4.80% . Twitter shares did gain about 7% in after-hours trading Friday. The stock is up 3.5% in the year to date and more than 8% over the past year.