Time and again there are men asking whether shaving their facial hair will result in a thicker beard down the line. The quickest answer I can give you is, no. Shaving will not make your beard thicker.
Shaving will not hurt or improve your beard growth, so while I would recommend not shaving if you want to grow a beard (uh, right), it's also fine to shave if you need to. Say, for your job. If it came in once, it can come in again. That's an answer to a question that comes up from time to time, especially from those using minoxidil to grow their beards.
The hair follicle is what determines the thickness of your hair; the more follicles you have, the thicker your beard will appear to be. The thicker each individual strand of hair, the thicker your beard will appear to be. This follicle is underneath the skin, similar to a plant's root being under the ground. Shaving the hair is simply cutting it, creating a blunt edge. When the hair then starts growing back out, our perception of it being thicker is because of its edge, as well as the fact that shorter hair is stronger than longer hair, giving the appearance of thickness and the feeling of strength. The contrast between your hair and skin also differs when the hair is shorter like that.
Ever wonder why full beards look fuller after they're trimmed and lined? It's an illusion, the same way that seeing thicker hair after shaving is:
At the base of the follicle, the hair is at its thickest as it tapers off with length. When this hair is trimmed down close to the base, it's as if the hair is thicker than it was before.
On one last note,
The effect of repeated shaving on human hair growth was studied . . . No significant differences in total weight of hair produced in a measured area, or in width or rate of growth of individual hairs, could be ascribed to shaving.
- Journal of Investigative Dermatology, 1970 study
To grow the fullest beard that you can, keep what you're growing. Stop trimming (except for when it comes to split ends), and most certainly stop shaving.