So many people here mystify me. What conveivable reason can you have for disagreeing with the major British dictionaries as listed by myself here earlier? If THEY all say the word, 'whereabouts', may be treated as a singular OR a plural, how can YOU possibly claim it can only be plural? Is it simply because it has the letter 's' at the end? Bus ends in 's', but IT'S not plural, is it?
As further evidence, here's what Fowler's Modern English Usage has to say about whereabouts...
"The word is plural IN FORM but is construed EITHER as a plural OR a singular noun."
(The capitals are mine, of course, for emphasis.)
It is perfectly plain that every authoritative source on the use of our language disagrees with you. None of them say you can't treat the word as a plural, but - by the same token - you most certainly are in no position to say we can't treat it as singular.