‘Angry Birds’ Maker Rovio’s Shares Drop 45% After Revenue Warning

Shares in Rovio Entertainment Ltd. fell by more than 45% on Thursday after the company behind the “Angry Birds” mobile-gaming franchise missed fourth-quarter sales expectations and warned revenue would be flat or lower in 2018 as it struggles to bring in and hold on to new players.

The stock market rout pushed shares to less than half their September initial public offering price. The selling comes three months after Rovio reported disappointing earnings in late November, promoting a more than 20% fall in shares that day....