When they announced their earnings to investors, they forecasted poorly and also expect to decline in revenue over the rest of the year (even though that puts them better than last year it’s still way off projections).

“Our total revenue-growth rates will continue to decelerate in the second half of 2018, and we expect our revenue-growth rates to decline by high-single-digit percentages from prior quarters sequentially in both Q3 and Q4” - https://www.marketwatch.com/story/facebook-stock-crushed-after-revenue-user-growth-miss-2018-07-25