Fewer and fewer teenagers using Facebook: Report

Facebook's losing its cool—again.

A report by Frank N. Magid Associates found only 88 percent of social media users in the U.S. between ages 13 and 17 use the social network, according to Bloomberg. That's a big drop from the 94 percent of users in the same age group last year. In 2012, some 95 percent of social media users in that age range were on Facebook.

A spokeswoman for Facebook declined to comment, Bloomberg said.

At the same time, usage on Twitter climbed 2 percentage points to 48 percent among users in the coveted teenage demographic, according to the report.

Facebook's popularity slips

So what's behind the drop? Only 9 percent of those surveyed in the report think Facebook is trustworthy. Others said they had more fun on competing networks such as Pinterest.

Read MoreWhen will Facebook have more dead than living users?

Compared to newer social networks such as SnapChat, the user base on Facebook has been trending older for the past few years. But Facebook received some good news on Friday—Instagram, the photo-sharing app it purchased in 2012 for $175 million, was valued at $35 billion by Citigroup.

Here's the full story in Bloomberg.