These are the eastern leaffooted bug nymphs. They have piercing-sucking mouthparts which they use to extract juices and nutrients from the developing tomatoes. Their feeding will cause the formation of tough, white tissues (like scar tissues) within the tomatoes. They are harmless to humans, so you can either knock them off and step on them (they will have a stink bug-like odor). They would also be susceptible to insecticidal soap which would not leave any toxic residues that you would have to wash off the tomatoes when you harvest them.  Most commercial producers would use one of the pyrethroid insecticides (the active ingredients will in in -thrin, like permethrin, bifenthrin, resmethrin, etc.). If you spray one of the pyrethroids, the tomatoes should be carefully washed before consuming. The pyrethroids are not systemic like some of the other insecticides. Systemics are not recommended for fruits and vegetables as the residues get into the tissues of the plant.