NEW YORK — Cracking down on hate, abuse and online trolls is also hurting Twitter’s standing with investors.

The company’s stock plunged Friday morning after it reported a decline in its monthly users and warned that the number could fall further in the coming months. The more than 17 percent drop in share value at the opening bell comes one day after Facebook lost 19 percent of its value — its worst trading day since Facebook went public in 2012.

Twitter says it’s putting the long-term stability of its platform above user growth. That leaves investors seemingly unable to value what the biggest companies in the sector, which rely on their potential user reach, are worth.

Twitter had 335 million monthly users in the quarter, below the 339 million Wall Street was expecting, and down slightly from 336 million in the first quarter.

The company said its monthly user number could continue to fall in the “mid-single-digit millions” in the third quarter.