Shares of Tencent Holdings and other prominent Chinese video-game companies plunged in Hong Kong trading on Tuesday after a Beijing-affiliated media outlet called their products “spiritual opium.” The blast from the outlet, Economic Information Daily, followed months of increased pressure from Beijing aimed at the broader Chinese internet industry, which serves one billion users. That pressure has moved global investors to pull billions of dollars out of Chinese technology stocks, on fears that tighter regulation could hurt company prospects. The Economic Information Daily article did not declare that any specific policy changes would be made, and it was unclear whether...