I want to be able to look for documents that contain a specific email address. 
I have tried searching for "johnsmith@abc.com" on Google, but I get no
results and suppose that they don't support that syntax.  I would like
the syntax and Internet search engines that support this type of
search.

Google canīt allow looking for attribute "@" mainly in documents.
It is because of spam.

Not true - the syntax is supported. Use this search string in Google
as proof - it returns only PDF documents containing the "help" address
for Google.

"help@google.com" filetype:pdf

Not specifying a filetype also works fine, whether or not you put
quotes around your email address.

I would also try searching substrings in your original address. Try
searching separately for text to the left and right of the '@'.

Also remember that while Google is indeed king of the search engines,
the others still work pretty darn good, and all rarely show identical
results. Try Yahoo (www.yahoo.com) and MSN's search (search.msn.com)
as well. My own testing between these two and Google gave different
results for each one.

If these suggestions return nothing, you may be out of luck with the
address find, and may have to use other information about this person
in order to "find" them.

Thanks,

Andy
http://www.andybrain.com