Tomato plant stunted
We think your plant may be showing signs of herbicide injury. Very small leaves, and the twisting and deformation of new leaves are common symptoms. The damage usually results from drift from 2,4-D herbicide. The active ingredient can drift a long distance on air currents before settling onto land. Affected plants very rarely grow out of the injury caused by growth-regulator herbicides.
In some cases the herbicide causing the injury is in compost or manure that was applied to the garden. If you suspect that might be the case, please perform a bioassay to rule out this possibility.
It's not too late to replant. If you cannot find tomato plants ask neighbors to donate suckers from their plants. You will need to water suckers regularly to get them established in your garden.jt
This makes me wonder if I caused the problem by using grass clippings as a top-dressing mulch? I applied Scotts with "Halts" crabgrass preventer to the lawn earlier this Spring. Could the grass clippings contain the herbicide that might be causing the damage to my tomatoes?
If your herbicide application contained 2,4-D this may have been a factor. However, if the herbicide was pendimethalin that was most likely not the cause.
If you did not add compost or manure to your garden this season as mentioned in this article http://extension.umd.edu/learn/gardener-alert-beware-herbicide-contaminated-compost-and-manure, then you should suspect herbicide drift.