Too much moisture, not enough nitrogen and growth would increase with more root space so yes, they definately need a bigger pot.. I grow 100 tomato plants from seed each year and keep them in quart sized pots for quite awhile, just have to make sure they are getting enough light, nutirents and containers need holes in the bottom for soil to drain. I report in a 50/50 organic soil, vermiculite mixture to allow for easier root expansion. Get that poor little mater pkant outside where it can thrive! If it is an indeterminate variety, don't forget to cage or stake it.