Facebook (NASDAQ:FB) recently started testing out disappearing messages on its Messenger app for select Android and iOS users in France. In a press release, Facebook stated that "disappearing messages give people another fun option" for communicating on Messenger. However, Facebook didn't state if it will test the feature in other countries.

Source: Facebook.

Disappearing "ephemeral" messages aren't anything new. Snapchat, which Facebook tried to buy for $3 billion two years ago, gained over 200 million monthly active users (MAUs) with its self-destructing messages. Line, which has 212 million MAUs, recently introduced encrypted "Hidden Chats" that disappear after a certain amount of time. Tencent's WeChat, the top messaging app in China with 600 million MAUs, has let users recall sent messages since 2014. So, why does Facebook Messenger, which has 700 million MAUs, still lack this popular feature?

Fits and starts in ephemeral messaging
Facebook tried to challenge Snapchat before. Back in December 2012, Facebook launched its Snapchat clone, Poke. Many people speculated that Poke could crush Snapchat, but the app never took off and Facebook quietly killed it off last May.

Shortly afterward, Facebook launched Slingshot, which Mashable's Karissa Bell called a "prettier, more desperate version of Snapchat." But unlike Snapchat, Slingshot didn't require users to approve connections. Facebook claimed that approvals weren't necessary because users could simply ignore messages, but it was an unusual move that indicated that Facebook didn't want approvals to throttle user growth.

Slingshot. Source: Facebook.

Facebook hasn't released official user numbers for Slingshot, but it seems tiny compared to Snapchat. On Google Play, Slingshot has only been installed 500,000 to 1 million times, compared to 100 million to 500 million installations for Snapchat. Therefore, it isn't surprising to see Facebook pivot away from Slingshot and integrate ephemeral features into its more popular Messenger app instead.

Why ephemeral messages matter
Ephemeral messaging matters because it's tremendously popular with younger users. According to Pew Research Center's data from earlier this year, 71% of teens use Facebook, 52% use Facebook's Instagram, and 41% use Snapchat.

Facebook needs to stay relevant with younger users because its core site is shedding younger users, particularly teens, while gaining older ones. Back in July, BI Intelligence asked teens which social network was the "most important." Between spring 2014 and 2015, the percentage that answered Facebook fell from 23% to 14%. Instagram's percentage rose from 30% to 32%, while Snapchat's surged from nothing to 13%. This shift indicates that teen users are retreating to alternative platforms as their parents start monitoring them on Facebook.

With millennials, IAC's (NASDAQ:IAC) Tinder, which streamlined speed dating, is another popular app. In January, Tinder acquired ephemeral messaging app Tappy to complement its service with disappearing photos and messages. Facebook noticed Tinder's growth and agreed to link its Instagram accounts to the service in April. In addition to enhancing Tinder profiles with Instagram photos, Tinder's linked profiles also reveal all of a user's Facebook's interests instead of mutually shared ones. That move ensures that millennials, who are less fickle than teen users, remain tethered to Facebook's ecosystem.

Third time's the charm?
Adding ephemeral messages directly to Messenger makes more sense than launching stand-alone apps like Poke and Slingshot. Both apps tried to build user bases from scratch, which was tough when many users didn't even know the apps existed. Messenger, however, already has a captive audience because Facebook forced users to download the stand-alone app last year.

Facebook subsequently added new features to Messenger, like payments and apps, to expand the app into a monolithic chat platform. That's similar to Tencent's strategy with WeChat, which lets users book taxis, play games, and buy things directly from its app. Bolting on ephemeral messages as a feature instead of focusing on them in stand-alone apps could help Facebook slowly siphon users away from Snapchat.

Yet I doubt that ephemeral messages, if Facebook expands them beyond France, will ever threaten Snapchat's growth. However, they can enhance Messenger as a platform and make it a more attractive all-in-one competitor against monolithic rivals like Line and WeChat.

Leo Sun has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Facebook. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.