One of the most common expressions people use is "fruitlessly." It means you have done everything that can be done to achieve a goal, and it hasn't worked. "Fruitlessly" may be used when trying to achieve any goal, but it is especially common in areas such as love and job hunting.

The dictionary defines "fruitless" as follows: "the failure of a search, an operation, or a plan to produce the intended result" (Webster). It is usually used to describe a situation when you have tried to do something, but it has not worked.