As others have said, the Creative Commons licences are generally thought to be better for non-code forms of expression, because the distinction between source and executable form (which the GPL uses a lot) doesn't exist for simple written materials. Before the CC licences were created, the FSF made the GNU Free Documentation Licence specifically to cover written content (some of my earliest photos submitted to Wikipedia were submitted under the GFDL). Before that (2000), people used to use the GPL for non-code content all the time, because there were no alternatives. It wasn't great, but I'm not aware that it ever led to disaster.
can [I] use a GPL license for the articles I write?
First and foremost, you can use any licence you like on content you create de novo.
That said, there is no bar on using the GNU GPL for your non-code material, should you wish to, but CC-BY-SA is designed to achieve the same ends in a less confusing manner. The FSF regard CC-BY-SA-4 as one-way compatible with the GPL3, so your choice wouldn't prevent people from later reusing your content as part of a GPL3-covered work.
What happens if I write an article and I state that it is licensed under GPL for example?
It means people can use, copy, modify, and distribute modified copies, of your material, subject to the conditions laid out in the GPL.
Does this mean that the site itself or the other articles become licensed under GPL?
Generally, no, it doesn't. This is one of the really misunderstood things about the strong copyleft licences, and leads people to use strong words like viral to describe them. Au fond, strong copyleft terms on content means that if you use that content as part of a work you're creating in a way that makes your work a derivative work of the content, you must distribute your work under those strong copyleft terms.
Works that happen to share a common distribution platform are not derivatives of each other, so the question doesn't arise. The code that forms the distribution platform's engine is not a derivative of the content it distributes, so the question doesn't arise.