A failure to properly monetise its mobile platform has always been Facebook’s Achilles heel, so it’s no surprise that it has just acquired another mobile-based company.

Social gifting app Karma has become Facebook’s fifth mobile buyout so far this year, though the news was somewhat overshadowed by Friday’s IPO.

It follows the acquisitions of mobile companies Instagram, Lightbox, Tagtile and Glancee.

The trend is easy to spot and signals that Facebook apparently doesn’t trust its existing team to drive mobile revenues. New data from comScore shows just how important mobile is to the social network.

Average U.S. users spent 441 minutes accessing Facebook from mobile devices in March compared to 391 minutes for desktop/laptop use.

Facebook now says it has 488m mobile active monthly users, a 14% increase from December. In an effort to cater to these users Facebook recently announced plans to launch a mobile app store.

No doubt its new acquisitions will take pride of place when it goes live later this year.

The Karma buyout will also come as good news to gifting app Wrapp, which has recently embarked on a global expansion after achieving success in its native Sweden.

The two apps offer similar services, allowing users to send their Facebook friends gifts using their smartphone.

Karma hadn’t been a huge hit with consumers,  InsideFacebook reports it had clocked up less than 50,000 Android downloads, but Facebook obviously feels that the business model has potential.