Perhaps more important is the amount of revenue

Perhaps more important is the amount of revenue Facebook generates from each of its active users, a figure encapsulated by the ARPU metric. Between Q3 2017 and Q3 2018, Facebook increased its ARPU by 20.1%, and judging by the most recently released quarter, is on pace to repeat a similar level of growth. Increasing the ARPU over time is a sign that Facebook’s targeted ads are becoming increasingly efficient, and some think the company still has a lot more efficiency gains to be made. That’s helping drive the stock despite slowdowns in some of the other financial metrics.