According to The Google Operating System blog and Lifehacker, the plus (+) search operator used by many Google searchers is no longer available. Searchers now need to use quotation marks to ensure that word(s) appear in the search results.
“When you enter a search into Google, the search engine doesn’t just search for all the web pages containing your search terms; instead, it returns what it thinks is the best match based on hundreds of factors, and the resulting page may not even contain one or more of your search terms. To explicitly specify that you want the results to include a word, you used to be able to add the + (plus) operator to the front of a term (e.g.,
+hackintosh +lifehackerwould ensure both terms were in all results). Now, rather than adding the + operator, you need to wrap the word or words in quotation marks (e.g.,
"hackintosh" "lifehacker"). (Most likely this change has something to do with Google+ and it’s +mentioning convention.)”