I only received one of your pictures. In this one, you can see what appears to be the droppings (frass) of a caterpillar, which leads me to think HORNWORM. 

These guys camouflage themselves and you usually don't notice them until you see the damage, as they blend right into the plant.  

However, caterpillars tend to chew from the edges of the leaves, and these have hole in the center of the leaves. This leads me to believe they could be SLUGS.

Slugs are night dwellers, so you would have to look for them with a flashlight in the evening. Faint slime trails around the holes help to confirm the presence of slugs or snails (slugs with a shell on their back). You may have to take away their hiding places, such as boards lying on the ground where they retreat to in the daytime. There are a number of ways to try to trap slugs.

Check out the websites below on slugs:

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7427.html#DAMAGE

https://www.msu.edu/~atkinso9/pestsnailpage.htm

The following is a lot of information on both hornworms that I found on the internet. Compare the descriptions of the damage to your plant and see if you can determine which it is, slugs or hornworms.

• If you see an insect on or near your beloved tomato plants, don’t rush for the nearest insecticide. Many insects are beneficial to the garden or at least neutral. That insect may be feeding on the very pests you’re having trouble with. Even if you’re looking at an enemy, one insect does not make an infestation. It’s best to identify the intruder and the level of damage it’s causing before implementing steps in managing insect pests in vegetable gardens (hat tip to Cornell University).

• For a complete description of tomato pests, along with photos and more details on life-cycle and organic control, visit the Pest Problem Solver at www.PlanetNatural.com.

• Hornworms are many gardeners' least favorite pest. These huge, green caterpillars with a "horn" on their back ends eat both leaves and tomatoes. They work fast, too. Handpicking is the best bet in the home garden because you often discover the pests at harvest time when it's unwise to spray with chemical insecticides. (The "horn" is fierce-looking, but harmless.) If you prefer to spray, use Bacillus thuringiensis (known as Bt, and available as Dipel or Thuricide), a natural insecticide that requires no waiting between application and harvest. This form of Bt only infects caterpillars. It is most effective if used when the caterpillars are small. Bt can kill the larvae of all species of butterfly or moth, so be sure to use care during application to minimize drift.

• ­­The tobacco hornworm (Manduca sexta) ranges from southern Canada to Argentina. The range of the tomato hornworm (Manduca quinquemaculata), however, extends only from southern Canada through the southern United States.

• Hornworms feed primarily on solanaceous plants (those in the potato family). They include tobacco, tomato, eggplant, pepper and some weedy plants. Tobacco and tomato plants are preferred. Hornworm eggs are smooth, spherical and about 1/16shaped markings on each side; the horn is straight and black. Both species are about 3 to 3½ inches long when fully grown. These destructive caterpillars are so big — three inches long or more — that it would seem to be easy to control them just by picking them off. And so it is, sometimes. The problem is that their pale green color provides excellent camouflage, and the nymph and larval stages are far smaller and less obvious. If there are only a few, picking them off works well. (One site suggests spraying the plant with water, causing the caterpillars to, and I quote, “thrash around,” giving themselves away.) If there are more than a few, other measures may be called for. One of these is Bt, or Bacillus thuringiensis, an organic treatment that can control numerous other problems as well.

• Hornworms strip leaves from tomato vines. If a heavy infestation develops, these caterpillars also feed on developing fruit. Rather than bore into the fruit, they feed on the surface leaving large, open scars. Fruit damage, however, is much less common than loss of leaves. Hornworm damage usually begins to occur in midsummer and continues throughout the remainder of the growing season.

• Natural parasitism often occurs, where Brachonid wasps oviposit eggs into the hornworms, the larvae feed inside, and then pupate on the backs of the hornworms. These pupal cases are seen as white projections on the back of the hornworm. If parasitized hornworms are found on the crop, feeding will have ceased, so leave it for the next generation of beneficial wasps to hatch.

• Actively feeding hornworms may be handpicked from the plants. In a home garden, handpicking and destroying many pests is an effective control measure. In addition, beneficial insects are very helpful in controlling insects such as aphids, leafminers and hornworms. To avoid killing these beneficials, use insecticides only when necessary.

• Insecticides such as permethrin, cyfluthrin or bifenthrin are effective in controlling stink bugs, leaf-footed bugs, aphids, fruitworms and hornworms. Do not use permethrin on tomato varieties with fruit less than one inch in diameter. Carbaryl will control cutworms, fruitworms and hornworms.

• Bacillus thuringiensis (B.t.) products are natural  insecticides that contains spores of this bacterium and are used to only control caterpillars (the smaller the better) when they feed on leaves with the spores. B.t. products such as Dipel (dust) and Thuricide (liquid concentrate) are effective in the control of hornworms and tomato fruitworms. Sprays give better coverage and stay on the plants longer than dusts.

• Spinosad is a natural product for the control of caterpillars and thrips. Pyrethrin is a natural product for the control of aphids and caterpillars. Adequate coverage of upper and lower leaf surfaces with these insecticides is important for good pest control.

If you use any kind of spray, organic or not, follow the directions exactly. Read the directions three times: before you make a purchase, so you know what you're getting; before you use it, to make sure you use it correctly; and after you've used it, so that you store it properly.

I hope this was helpful. Feel free to contact us again if you have further questions.

Happy hunting.