If you have a specific source you have found via a search engine, cite it as a standard Web source, using last name and page number, if available. A quote from page 42 of John Smith's online book, then, would be cited as (Smith 42). Without the page number, you can use only the last name (Smith) -- and without the last name, use the article title instead: (Article Title). Use this method to cite the search engine itself, for example: There are about 120,000,000 results for the name James (Google Search).
On the Works Cited page, you can omit the last name if you do not have it, for example:
Last name, first name. "Article Title." Website Name. Date published (day,
month, year). Web. Date accessed by you (day, month, year).
In citing a search engine, use this method:
Google Search. Google. 30 May 2013. Web. 26 May 2013.