SpriteBatch just sets up an order of things to draw, like a significantly fancier version of Java's Queue. If you have not already, you should attach your SpriteBatch to a Stage. Also, you should add your Actors to Stage, not SpriteBatch. Otherwise, a SpriteBatch carrying no references to any Drawable objects will do nothing.
If you only have a few Actors, I think you could call
draw() on the Actors themselves, which you probably lack here, but I highly suggest using Stage for that as well.
While you do not indicate using Scene2D, the code in the following section should still help:
https://github.com/libgdx/libgdx/wiki/Scene2d#viewport