(Bloomberg) -- Shares of AMC Entertainment Holdings Inc. surged by the most in six months after investors piled into bullish bets on the stock.

The movie-theater operator -- one of the poster children for the meme-stock mania of 2021 -- skyrocketed 27% Thursday to $9.15, its biggest jump since May 12. Trading activity in call options was triple the average over the past 20 days, with investors snapping up contracts that were out of the money earlier this morning.

Calls that expire on Friday with strike prices of $8, $8.50, and $9 were the most actively-traded AMC contracts on Thursday. All told, more than 550,000 calls traded as of 3 p.m. in New York, compared with a 20-day average of roughly 163,000. The stock closed at $7.23 on Wednesday.

Day traders also electrified social media chatrooms and message boards touting the shares. Thursday’s rally came as the “AMC” ticker symbol was trending on the popular trader chatroom Stocktwits, and it was among the most mentioned on Reddit’s WallStreetBets forum. However, buying demand from retail traders was lackluster. Individuals on Fidelity’s platform were net sellers as of 2 p.m. in New York. 

AMC Entertainment attracted individual investors over the past two years as they sought to rail against short-sellers who bet that share prices will decline. More than 20% of AMC shares available for trading are currently sold short, financial analytics firm S3 Partners data show. The stock is down 50% this year after a nearly 1,200% surge in 2021.

Other retail-trader favorites also advanced, with Bed Bath & Beyond Inc. gaining as much as 13% and GameStop Corp. rising 4.9%. The S&P 500 Index was up 0.1% as 3:09 p.m. in New York, while the Nasdaq 100 climbed 0.4%.

--With assistance from Matt Turner.

©2022 Bloomberg L.P.