The quickest way to get nutrients into a plant is to spray the leaves with a suitable plant food.
This may not necessarily be tomato feed as there are other nutrients that can help the development and growth of plants.
Seaweed extract is a great way to give your plants a boost - it's organic - and can be given by foliar spray or roots. It is particularly good when transplanting to bigger pots to stop plants from becoming stressed.
To help avoid blossom end rot in medium and larger varieties, a foliar spray can aid nutrient intake - calcium is crucial when plants are growing fruit - and give the tomatoes the food they need as fast as possible.
It is important to check the instructions on your plant food container to make sure that foliar feeding is possible - some feed is not suitable.
The best way to feed is little and often so that plants always have access to some food. My preferred method is to reduce the recommended amount by half and feed twice as often.