Yep related to squash bugs and stink bugs and are pretty stinky themselves -- they suck on the tomatoes like the stink bugs and cause similar damage.
Pick them off and look for eggs. Watch out for hatching event and get the nymphs while they are still congregating and slow. They are soft-bodied and more vulnerable to sprays than the nearly indestructible adults -- those are better dealt with the boot-heel. I'm out of practice but had the snatch, toss on ground, and stomp perfected to smooth fluid motion last summer.