The simple answer is that "so many" *didn't* buy after earnings. FB *gapped* up, it didn't *trade* up. It was pushed way up high by hedge funds in relatively low volume extended hours trading in order to sucker in more bagholders. The actual trading activity has trended consistently down almost from the opening bell after earnings.
*shrug* I appreciate it, to be honest. I closed my short position the Friday before earnings, and the ridiculous gap up gave me a gift-wrapped opportunity to re-short. It's very rare in the stock market to get a trading opportunity this obvious. I booked partial profits this afternoon to guarantee a gain even if by some odd alignment of the stars FB goes back up and my puts expire worthless, but I'm still holding 2/3 of the original position, because there's plenty of more downside left.
Finally a smart trader on this board who knows how to make money! I agree it was a gift. We went from 19 to 24 right back down to 19. If I were you I would be ready to cover your short or at least put in a stop at just over $20 so you don't give up some nice gains. From the chart, it looks like FB will re-test 18 and possibly break the 52-week low, but be careful. Everyone and his brother is expecting the lock-up expiration to send this stock lower, and it should, but with the recent sell-off, don't be surprised if it works it's way back to 24 by December once all the sellers have sold.
hedgehog, i'm more into lnkd but I think you might be onto something. On low volume days I see some pretty funny things happen. And after hours is unbelievable. I don't even think you need hedge funds. Just two guys who agree to trade the same 500 shares back and forth at particular times. Several times I have seen a trade that was 2 or 3 dollars higher than the prevailing trade and that's the one yahoo finance is showing as the latest trade.