Some online journal articles don't include page numbers, which makes citating them tricky. If you can't locate page numbers for a specific passage in article you want to cite, a good practice is to try to include information that will help readers find the passage being cited. One way to do this is to indicate the paragraph you got the information from. For example:
Miller (2007) asserts that "sleeping disorders are common among women over the age of 50" (para. 9).
When including such an article in your list of references, cite without page information. You will want to include the URL from which you got the article, however. Here's an example:
Kenneth, I. A. (2000). A Buddhist response to the nature of human rights. Journal of Buddhist Ethics, 8. Retrieved from http://www.cac.psu.edu/jbe/twocont.html