If I post a poem on my facebook site and someone cuts and pastes it on their site is that a case for stealing my intellectual property

If the poem is original with you, then yes. Did you copyright it?

Write "Copyright 2011" at the bottom of it and then follow directions in one of these: http://www.google.com/search?q=how+to+copyright&ie=utf-8&oe=utf-8&aq=t&client=firefox-a&rlz=1R1GGLL_en___US379