TechCrunch did some math on this and figured out, if the network keeps its popularity and revenue up, it would make $4.69–4.81 per user annually. Doesn’t sound like much, but again — when you’re talking about 900+million accounts, that’s not exactly chump change.
As for how it’s earning these coins, most of the credit goes to, of course, advertising, which accounted for $872 million. Facebook credits and payments, however, are accounting for a bigger portion, going from $94 million last year to $186 million.
For more about Facebook’s earnings and other financial notes, hit up the source link.