Pinterest (PINS) shares dropped more than 12% in extended trading after the company issued a disappointing first-quarter forecast.

Fourth-quarter revenue reached $1.32 billion, missing the consensus estimate of $1.33 billion. Adjusted earnings per share of $0.67 fell just short of the expected $0.68.

Management projected first-quarter revenue between $951 million and $971 million. This guidance trails the $981 million expected by Wall Street. The outlook highlights challenges in competing for advertising dollars against larger rivals.

Global monthly active users rose 12% year-over-year. The platform reached a record 619 million users during the quarter.