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We know "among", but do you know "among of". I used to use it, but my friend says it's wrong.
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It sure sounds like it would be wrong, but why don't you show some of the sentences you would use it in, and let us see?
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To me, among of seems very strange, and doesn't say anything extra in comparison with among.

It can be replaced by among in each and every of these examples taken from the New York Times (which show it is currently being used, unfortunately):

http://query.nytimes.com/search/query?query=%22among+of%22+&srchst=nyt