Your tomatoes need plant fertilizer to grow, flower and produce tomatoes. Tomatoes also have a great need for magnesium and calcium and can suffer from deficiency diseases such as pestilence. Therefore, check that your plant fertilizer has magnesium and calcium in it. The nutrition ratio often varies between different producers, here is one example:
3% Nitrogen (N)
1% Phosphorus (P)
5% Potassium (K).
The rest of the fertilizer consists of other macro- and micronutrients, like Calcium, Magnesium and sulfur.
Nitrogen (N) - gives good growth and fresh green leaves Phosphorus (P) - promotes good budding and rich flowering Potassium (K) - helps the plant build strong stems and a strong root system