Sorry VeroHerrera, but your statement is incorrect. There is a big difference between To be employed by and to be employed with.
To be employed by means that someone gave the employment to you. It`s passive voice and therefore you use "by" (e.g. Stephen's father employed me last week= I was employed by Stephen's father last week).
To be employed with, as emsr2d2 said, gives you the impression that you got the employment at the same time another person did so. Thus, you can notice an enormous difference between both expressions. The preposition "with" can be used in other ways to express the same, but it definitely cannot replace "by" in that sentence.