Actually you could use the NN to find a function minimum, but it would work best combined with genetic algorithms mentioned by Erik.
Basically NN tent to find solutions which correspond to a function local minimum or maximum but in doing so are pretty precise (to comment on Tetha answer stating that NN are classifiers you can use if to say it the data input is minimum or not)
in contrast genetic algorithms tend to find more universal solution from the whole range of the inputs possible but then give you the proximate results.
The solution is to combine the 2 worlds
- Get the approximate result from genetic algorithms
- Use that result to find the more precise answer using NN