If possible invest it in an existing company Facebook can't compete with, for example Wechat/QQ. Use the money to strengthen it's position in neighboring countr

If possible invest it in an existing company Facebook can't compete with, for example Wechat/QQ. Use the money to strengthen it's position in neighboring countries where it is competing directly with Facebook and to try to enter poor markets where Facebook doesn't yet have complete market domination (think the places where Facebook tried to introduce Free Basics).