Shares of Helios & Matheson Analytics Inc. are up 15% in Tuesday morning trading after the company said in a filing that Ken Griffin's Citadel Securities had amassed 5.4% of the company's common stock as of Friday's close. Helios & Matheson is the majority owner of movie-ticket subscription service MoviePass. Shares have tumbled in recent weeks after the company issued an update on its cash balance. The company recently reported an earnings beat and said that it was "naturally seeing significantly reduced usage [of the MoviePass] over time" and that efforts to curb abuse of the system weren't impacting new memberships. The stock is down 80% in the past months, while the S&P 500 has gained 0.7%.