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Mike D from the Beastie Boys ﻿told cops he's out thousands of dollars in surf and skate gear and now police are on the hunt to catch the thief.

Law enforcement sources tell TMZ ... L.A. Sheriffs Dept. got called to the Beastie Boy's home Friday after Mike D claimed someone broke into his outdoor storage shed at his Malibu pad where he had loads of surfboards, skateboards and other miscellaneous surf gear.

Mike reported that around 15-20 surfboards were part of the heist ... and 3 were worth $1,000 each.