When Facebook Inc. (NASDAQ:FB) disclosed its third-quarter earnings a couple of weeks ago, David Ebersman, Facebook’s chief financial officer, noted that the Menlo Park, Calif.-based social network had seen a decrease in daily usage among teenagers. It turns out that more and more young users are instead communicating with each other on mobile messaging apps like WhatsApp, LINE, Kik and others.

WhatsApp now has more than 350 million active users, making it the world’s most popular messaging app, with even more active users than Twitter. The Guardian estimates that WhatsApp is on more than 95 percent of all smartphones in Spain and that the majority of those users are under 25.

Facebook, it seems, just isn’t cool anymore. While Facebook is proud of its 1.2 billion monthly active users, younger people are becoming less active on it because they don’t like their news feeds filled with updates about their aunt and her cat, or having their parents “Like” everything they post.

Messaging apps are more private. It’s safer and more intimate to share a status, picture or video through a private message than to post on Facebook.

Just look at the success of Snapchat, which deletes an image or video just a few seconds after it's seen, allowing teens (or anyone) to send images that won’t be permanently recorded online. Snapchat now has about 5 million monthly active users and is valued between $2 billion and $4 billion.

Messaging apps have become so popular, they're now like social networks in their own right and boast features beyond simple messaging. Kakoa Talk in South Korea, WeChat in China, LINE in Japan and Kik in Canada allow users to send stickers, play games and share music. These features have generated millions in sales. Though WhatsApp sticks to just messaging, it's rolling out an API to make it easy for users to share content through WhatsApp, sort of like the Facebook “Like” button you see on every website.

Facebook tried to downplay the trend, saying it’s difficult to get accurate metrics on young users. But it's clearly trying to jump aboard, giving its own Messenger service more attention lately, including a redesigned stand-alone app.

With its reported $425 million earned in the previous quarter, it’s doubtful that Facebook is too worried at this point. But with more and more young people using messaging apps instead of the social network, it can only be a matter of time before older people catch on as well.

Do you use messaging apps instead of Facebook? Let us know in the comments.