Try some BT. There's lots of brands and it's inexpensive. Have you seen the bug? Is it green with a horn on the back?

I agree with Tracy. It sounds like good ol' tomato hornworm (though it might be something else, but they are the first thing to come to mind). They are caterpillars that start small but become almost hot-dog sized before they pupate and turn in to those beautiful hovering "hawkmoths" or "hovermoths".

Bt is bacteria that will kill all caterpillars and it is quite effective.

I grow tomatoes in winter and spring when the caterpillars aren't much of a problem. In summer I do get them on my datura foliage but I like the moths so much I tolerate them (sorry anyone nearby who grows tomatoes, LOL). You can also pick them off and squish them, feed them to the birds, or drown them in soapy water.

Let us know if you get a definite ID and what you do and how it works. Good luck saving the rest of your crop!

Take care,
Grant

Here is a link that might be useful: {{gwi:406447}}