This happens to me every year (until I wise up, and get out the fencing). We have groundhogs, and I have seen them eat the neighbor's tomatoes, even the green ones.
I wonder if deer also eat them? We definitely have deer damage on the surrounding vegetable plants, but they usually nip the leaves off.
I bought the green plastic fencing mesh on a roll at Home Depot--about $7-8 for a small roll--thinks its either 25 or 50 ft long, about 3 ft high--but comes in larger sizes. I jam poles, such as the bamboo stakes they sell in the garden center--about 5 ft long, though the mesh, then into the ground. Do it as much as you need to support the "fence" sections, and put it around your plants. Make sure the mesh is not the big, 3"x 3" or bigger mesh--the smaller, the better. You just weave your poles through the mesh in a number of places around the piece you cut. You may need wider fencing. The bottom edge of mine goes to the top of a built-in planter, which is 12" tall. Or, just use 2 pieces, 1 on top of the other (which you can cut to size) and get longer poles.
You could do this with chicken wire, too, but that's nasty to work with, and I don't like the silver color, andI think it may be more expensive (?).