A tomato fertilizer is rich in potassium and that makes it perfectly suitable for using on strawberry plants. Such a feed on strawberry plants that are growing in pots or containers every week or two from early spring onwards will boost flowering and the setting of fruit.
An example of such a tomato fertilizer is Jobe's Organics Tomato Slow Release Plant Food available from Amazon. Though, any fertilizer designed for usage if you are growing tomatoes will be ideal for using on any strawberry plants.