What type of screw is used for 2007 Kia Optima wheel well?

It is sometimes referred to as inner fender. My front passenger wheel well lost a screw and I couldn't find a match at my auto part store and everywhere else says that the screws come with the molding, but I don't need the molding, and they also don't mention specs of the screws.

All I know is that it is plastic and uses a phillips head. Also, the screws in the back are different than the front, or is there suppose to be some nut to hold it in place?