How to search the set of papers whose references contain a given preprint? I am reading a preprint titled Combinatorial Group Theory In Homotopy Theory I by Fred Cohen (available at Cohen's web page)
Now I need to find all papers whose references contain this preprint. Is there any way to do so? (By the way, I have access to Mathscinet.)

Google "Combinatorial Group Theory In Homotopy Theory I" and go through all the links you got (about 4 pages worth). This might not give you all the references, but, probably, most of them. 
