I've had a garden for 3 years now, zone 10, and this is the first year I've been plagued with something eating almost everything. Whatever it is, they've eaten parts of the following:
small green tomatoes (I know birds get ripe tomatoes, but eats them while they're still green!)
papaya tops and leaves of seedlings
pecans (squirrels undoubtedly)
I have seen opposums in my yard, racoons, squirrels, grasshoppers, snails; my neighbors have had rats in their garden, so I'm sure, after 3 years, they've found mine by now.
Between one of my neighbors and myself we've gotten rid of the grasshoppers and snails from our immediate area, so now I'm not sure what is eating what. It's a container garden on concrete blocks 3 blocks high.
my neighbors have lost pomegranates; so far mine are still on my bush, yet-to-be-tree.
On your small green tomatoes, look for little caterpillars.
Raccoons like watermelon, so do opossums and my neighbor's dog.
I've had sphinx moth caterpillars eat the papaya leaves, but they don't eat enough to really hurt a large plant.
You don't really say if the pest is eating just the fruit of the plants, or leaves, too. I've watched squirrels pick and eat my tomatoes and strawberries. And a chipmunk climbs my peach tree and blueberry bushes and eats the fruit. My husband had good luck spraying our magnolia tree in the spring with deer/rabbit repellant and that kept the squirrel from eating the blossums of the magnolia. But it smells awful (urine), you wouldn't want to spray it on your tomatoes.