Might be caterpillars. There are a number of them that are very good at disguising or hiding. I look carefully on undersides of leaves for bright lime green ones that hide along the ribs of the leaves, and there are also hornworms that are camouflaged as well. Another is armyworms/climbing cutworms that will often hide themselves in loose soil near he base of the plants, or hollowed out spaces in developing fruits. All start out very small and can get pretty large. I just remove &/or smash them.

Pics might be helpful...

Look under the leaves for green tomato hornworms, and also go out at night and look for them. They can strip a plant overnight, but they're hard to spot because they're the same color as the leaves.

Carol: I tried posting a photo but couldn't get it to post...it just hung there forever, so I gave up and posted w/o the photo.

Try posting in a comment and be patient if it's a big file &/or you have a slow connection.

Or you can resize the photo

Latest report: I found well-formed scat this a.m., and according to photos found online the scat is from hornworms. However, I went out shortly after dark last night but could find no sign of the critters themselves. Am in the process of trying to find a UV flashlight so that "search and destroy" method will work after dark.