If would you like to find file that contain a specific string

open cmd.exe and digit:

findstr /M /S yourtext .\*

/S Searches for matching files in the current directory and all subdirectories
and /M prints only the file name if a file contains a match

This command search string in all files, If would you like to find file with specific extension

findstr /M /S yourtext .\*.vb

This Searches only file with .vb extension

For more info about this command and to see all its parameters
Click here