In case you're trying to search recursively for a specific file type and data mask, grep -r is not enough to bring the desired result.
You'll have to use --include 'type' and then, even if the directory does not contain any of the given filetype in root, it's still working.
Example;
grep -r --include '*.extension' 'Text to match' directory
grep -r --include '*.cpp' 'Audio' .