GoPro Inc. GPRO, +0.57% warned investors that holiday sales were disappointing Wednesday and announced that it would cut its workforce by 7%, and shares dove more than 20% in late trading. The action-camera company said that it expects fourth-quarter revenue to be about $435 million, well below analysts' average expectations of $521 million, according to FactSet, and GoPro's guidance of $500 million to $550 million. While noting that its workforce had grown by 50% annually in the past two years to a total of 1,500 at the end of 2015, GoPro said it would lay off 7% of its workers, incurring a charge of $5 million to $10 million. GoPro stock has suffered a freefall after a booming initial public offering and early performance, declining 72% in the past six months. GoPro shares plunged more than 20% in late trading Wednesday after being halted, falling lower than $11 after closing at $14.61, a penny higher than its all-time closing low. The company expects to release full financial results for the fourth quarter and year on Feb. 3.