Has it been real rainy where you are? Purplish tomato leaves are usually an indication of phosphorous deficiency, which can be caused by a variety of issues including too-wet soil, cold soil temperatures, or phosphorous deficiency in the soil. If there's been lot of rain, my first thought would be that your problem is soil that is staying both cool and wet. When that happens, the plant isn't able to take up phosphorous from the soil as well, and the result is those purple-tinged, stunted leaves you mention. The good news is that the plant will bounce back on its own once things dry out a bit and the weather warms up.