This is a gag that has been pulled before (on someone else I think). Some guy (with bad taste in lawn ornamentation evidently) happened to hear a car drive in, looked out the window, and guys in ski masks were grabbing his lawn dwarf and speeding away before he could do anything.
Around a year later (if memory serves for all this), there was a knock on his door late one night. There was a bag which had the dwarf, plus numerous photos of the dwarf at various famous places, such as Stonehenge, Great Wall of China, whatever. What a weird hobby.
Of course, I also used to work with people who pulled a similar trick (not with a lawn dwarf, but rather some kind of goofy figurine he kept in his office) each time one of them took a vacation. Soooo, there wasn't much of a mystery to the disappearance. But it was pretty amusing.