Searching in InTouch has gotten better, but is still not up to what you are asking. In your case, finding a string, you will probably have to use the old fashioned search function.
First, create a "Generic Text Only" Printer on your system, and set it to print to FILE.
Then, Print out the entire InTouch project to that file.
Finally, open the text file in your favorite text editor (or notepad if that's all that's available) and search for the string there.
For the record, this used to be the only way to search for anything in InTouch, including tagname usage.
Good luck!