Facebook shares fell to a new low of $21.61 Tuesday, down more than 50 percent from its debut price of $38, though closed out the day at $21.71. UBS's US-traded shares fell more than 4 percent, closing at $10.60. (Click here for the latest after-hours quotes for FB and UBS.)

— Reported by Maria Bartiromo and written by Javier David. Reuters contributed to this article.

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