This is my first tomato plant, which I am growing in a hanging basket (big dog can't lift his leg to "water" it). It's a Patio Tomato. It was thriving and had several tomatoes on it. I check almost daily as I look for ladybugs, aphids, and other six-legged visitors. I thought I would have to compete with the birds for my tomatoes, and wouldn't have minded losing to them. But this monster, who wasn't there two days ago, destroyed four of my fruits! What is he and where did he come from? There are no other vegetables/crops anywhere nearby. This beast is about the size of my little finger! I had hoped to avoid the use of pesticides as I do so like to pick and nibble right from the bush and don't want to harm wildlife or good bugs.
That is a worm. Not sure which worm, but it will eat your plant down to nothing overnight.
Remove it by hand, squish it, and be on the lookout for any more.
A sure tell way to determine if there are more is by the black pellet poop these worms drop as they gobble up your leaves and fruits. If you see these black droppings on any leaves, search immediately ABOVE those leaves, looking on the undersides of the leaves above. Generally, they start with the most tender leaves at the very tip of a branch that will hold their weigh, then move their way down that branch toward the stem of the plant. Then, they begin again.
You can spray your plant with Bacillus Thurigiensis (Bt). It is considered an organic product. The worms have to eat the coated leaves first. Once the Bt enters their system, it does its thing on their intestines.