An attack on short positions by Reddit users continued for some stocks Thursday, sending their valuations soaring once again, while others trimmed recent huge rises.

The share prices of headphone-maker Koss Corp. and swimwear manufacturer Naked Brand Group Ltd. more than doubled in premarket trading, having already gained 1,538 percent and 203 percent, respectively, this week as hedge funds scrambled to close short trades on a number of companies touted on the WallStreetBets forum.

The most-prominent example of the recent short squeeze mania, GameStop Corp., see-sawed in premarket trading and was down 12 percent at 9:02 a.m. in New York. The stock has surged 1,745 percent this year.

XpresSpa Group Inc., an airport spa operator that pivoted to Covid-19 testing, surged as much as 48 percent as Reddit users dubbed it the “next short squeeze.” Other short favourites rising included biotech Cel-Sci Corp. and miner First Majestic Silver Corp.

Cinema group AMC Entertainment Holdings Inc., meanwhile, was down 20 percent, having erased its pandemic-induced plunge Wednesday with a 300 percent surge. Retailer Express Inc. slipped too following a surge this week, while Bath & Beyond Inc., and fashion firm Fossil Group Inc. erased declines ahead of the open.

By Joe Easton