Zynga's titles range from "FarmVille" to "CityVille" to "Words With Friends," the Scrabble-like game made popular on mobile devices.
Zynga shares fell 33 cents, or 12.6 percent, to $2.29 in after-hours trading. The stock closed up 11 cents, or 4.4 percent, at $2.62 in the regular session.
Facebook shares dipped 4 cents to $27.28 in extended trading. Its stock has surged by nearly 30 percent this month on increasing optimism about the company's ability to make money on the traffic visiting its service on smartphones and tablet computers.