I started to say they must be mealybugs - but then I realized they could be the mealybug destroyer larvae, too:

How to tell the good bugs from the bad bugs

Search on "mealy" to take you down to the entry on mealybugs vs mealybug destroyers.

Mealybug destroyer larvae get up to about 1/2" - about twice the size of mealybugs. If that's what you've got, good on you! (Copies Aussie talk because they are an Australian import - that works for the GOOD!)

There are some other beneficial ladybug larvae that look similar, this article discusses another species whose larvae look similar to the mealybug destroyer:

Scymnus ladybeetle article

Search on scymnus larva and click on that link to see a pic of that larva.

I can't tell from the picture - how big are these critters?

It sure looks like the larva of a mealybug destroyer, to me! Congratulations.

They eat aphids, too! If it's mealybug destroyers, that is.

Take a Q-Tip, put alcohol on it and touch the mealy bug or Mealybug Larva. If it is it will kill it. But not sure how to use it on a tomato plant. Never had it on a tomato plant.