There are many apps doing reverse lookup with their own databases which are often publicly searchable by Google. By doing a Google search the probability of finding the number is considerably higher since each of those databases contains only a certain set of numbers.
Q: It doesn't work.
A: Make sure you run the app after installation at least once otherwise it won't work.
Q: Will this app reveal hidden/blocked/unknown/unavailable caller numbers?
A: No. Maybe a service such as Trapcall can help with that.
Tip: You can then redirect these nuisance numbers to voicemail by adding these numbers into one contact with enabled option "All calls to voicemail". How to do it is described in:
Tags: reverse lookup, automatic caller search
If it works on your phone, consider rating this app to let me know that the app works on your phone model. Thank you.