Searching data of laravel meta table of type metable

I have 3 tables users, articles and metas. I had defined the morphTo() and morphToMany() according to the laravel 5.3 doc and I can pull any particular property of either the user or article defined in the metas table such as firstname or lastname or coordinate.

Now am having difficulties writing the correct model to search these properties e.g a search for any user's firstname or lastname or both.

via Chebli Mohamed