Snapchat may be losing ground to Instagram with some of its most important users: teens.

Instagram is now the most-used social media platform among teens, according to research firm Piper Jaffray.

The new stats show that the Facebook-owned photo sharing app is slowly gaining ground over Snapchat. Eighty-five percent of teens report using Instagram at least once per month, compared with 84 percent who say the same for Snapchat.

The findings, part of the firm's fall 2018 "Taking Stock With Teens" survey, is the first time Instagram has edged out Snapchat for the top spot. Though the two apps have consistently ranked at the top for teens, Snapchat has been slightly more popular since the spring of 2016.

It's not all bad news for Snapchat, though. Interestingly, the same report found Snapchat had a significant advantage with teens in likability: 46 percent of teens surveyed rated Snapchat as their favorite platform, compared with 32 percent for Instagram.

Still, declines in usage among teens would be a worrying sign for the company, which is already dealing with declines in usage following an unpopular redesign. If Snapchat is now losing its edge with teen users, one of its most important demographics, it would be a serious blow for the company.

There are troubling signs for Facebook, too. Even though Instagram is more popular with teens, Facebook is still wildly unpopular. Just 36 percent of teens report using the social network at least once a month and only 5 percent rated it as their favorite platform.