Sources Without Page Numbers
e.g., for articles in the journal PLoS ONE
When an electronic source lacks page numbers, you should try to include information that will help readers find the passage being cited. When an electronic document has numbered paragraphs, use the abbreviation "para." followed by the paragraph number (Hall, 2001, para. 5). If the paragraphs are not numbered and the document includes headings, provide the appropriate heading and specify the paragraph under that heading.... According to Smith (1997), ... (Mind over Matter section, para. 6).