The miticides that might control Spider Mites will also kill off any predators of these mites so they will be able to grow in numbers unhindered. Spider Mites breed faster in hotter, dryer, weather so misting the plants they are in can help keep numbers down. Some sources do recommend Insecticidal Soaps, which can also kill off predators of Spider Mites. Plants stressed by the weather are good targets of these wee buggers.
The attached link provides some very good information.

Here is a link that might be useful: About Spider Mites

Horticultural Oil if applied properly will always kill Spider Mites, adults, juveniles, and eggs. It will not kill any Mite predators including predatory Mites, which will then go look for other Mites to eat in your garden.
Conserve (spinosad) will reduce the populations but not control them.

Plants overwhelmed with pests are typically stressed even before the pests even arrived. The pests may deliver the final blow.

So, you need to spill the details about how you're growing your tomatoes. It's rather like playing 20 questions. The more you tell us, the more likely we can assist you.

Pots or the ground?
Watering? Method and how often?
Also how do you decide to water again?
Fertilizing?
What else can you add?