SAN FRANCISCO — For years, people seemed to have an unlimited appetite for signing up for social media services. Now some of those companies may be hitting a wall to adding new users.

On Tuesday, Snap, the maker of the Snapchat app, said it lost three million daily active users in the second quarter from earlier this year. It was the first time since the company went public in early 2017 that it had reported a decline in users.

Snap’s report follows similar trends from Facebook and Twitter. Facebook revealed late last month that its number of users in the United States was flat from earlier this year and that its users in Europe had fallen over the same period, even though its total number of members had grown. And Twitter, which has struggled for years to increase interest in its platform, also said in late July that its monthly active users had decreased by one million from earlier this year. After those disclosures, share prices of both Facebook and Twitter tumbled.

The declines and flattening growth raise questions about whether the social media companies have reached a saturation point in some markets, especially in developed countries. That may have been compounded by a steady stream of bad news about social media in recent months, which may have also deterred users. Facebook and Twitter have grappled with the spread of misinformation and foreign interference on their sites, for example, while Facebook has also been dealing with the misuse of user data.