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IAC, Match Group's parent company, dropped more than 17 percent.
Sparks Networks, owner of JDate and Christian Mingle, fell 7.3 percent before recovering and closing up 0.8 percent.
Match Group Inc shares closed down more than 22 percent.
A dating service could increase the time people spend on Facebook and be a "big problem" for competitors such as Match Group Inc, said James Cordwell, an analyst at Atlantic Equities.
Match, the owner of popular mobile dating app Tinder and Ok Cupid, calls itself the "global leader in dating" on its website.
It did not appear to have a feature to "swipe" left or right on potential matches to signal interest, as Tinder and other established services have.
But there were two buttons for "pass" and "interested." The optional feature will be for finding long-term relationships, "not just hook-ups," Zuckerberg said.