It searches wherever you have selected, the current directory. There are also 2 searches.
This is the first:
Type and it will search the current location, and select the folder with that name. If there are multiple with the same starting with the current search, it will chose the first by current sorting (alphabetically by default).
Then there is the real search, to search the folder and all files / folders in it:
To access this, click the search icon, in the top bar.
Here, you are searching "Home" by default. You want to search a different folder, so there are 2 ways to get that:
If you want to search from the root directory, all the computer (
/) click All Files.
If you want to search a certain folder, navigate there and then use the search tool.
Your question sounds like you want to search everywhere (although I'm not sure why). So click the All Files at the top, or click Computer at the side, and then do your search.
As an alternative, install
sudo apt-get install nemo
It is based on the same code as nautilus, but may work when nautilus doesn't.