The app is currently available only on Apple's App Store in the United States and Canada, according to data from industry site Sensor Tower.
Facebook's New Product Experimentation (NPE) team, which created Tuned, describes the app as "a private space where you and your significant other can just be yourselves."
NPE was created last year to focus on launching consumer-focused experimental apps. In February, the team launched a photo and video sharing app, "Hobbi."
Tuned is currently ranked No. 872 in the United States and No. 550 in Canada in the social networking category, Sensor Tower said.