Article is simply a publication. It may be for the purpose of propagating the news, research results, academic analysis or debate.
It is written composition in prose, usually nonfiction, on a specific topic, forming an independent part of a book or other publication, as a newspaper or magazine. - the definition of article
A blog is published through online medium and updated, like website or webpage imparting fiction and/or non-fictitious information to its readers. The main difference is that blogs are usually written in informal structure. Administrator may start real time debate under the blog.
Press release is an official statement issued to newspapers giving information on a particular matter. Press release is pre-formatted information about specific subject, product or operation of an individual or organisation issued to an editor in attempt to release newsworthy information to public.
A press release, news release, media release, press statement or video release is a written or recorded communication directed at members of the news media for the purpose of announcing something ostensibly newsworthy