Transfer the seedlings to their own pots when they start to grow their first true leaves - the ones between the seed leaves - see below:
Should Seedlings Be Fed?
If you use good quality new compost, you do not need to feed them until they are much bigger - when they start to fruit. However, they will need to be potted-on after about four weeks or so. That means more compost which contains more food.
If you want to feed them at this early stage, you could give them a "one off" feed - when potting-on - at half the recommended strength as on the box of general purpose plant food.
Tomato feed should only be used when the plants are fruiting because it contains mostly potash for fruit development and not the nitrogen and phosphorus for the growth of young plants.