See this demo file:
If you are using FileMaker 12 or newer, use Open from FileMaker's File menu to open this file and produce a copy converted to the newer file format.
The bottom left two "search portals" are examples of the type of searching that you want to do. It took a bit of trickery to get the portals to update properly with each keystroke without also bogging things down with a Refresh WIndow [Flush Cached Join Results], but the extra tricks may not be necessary if you do not use a global field for entering the search text.
After getting everything just like the demo, it worked perfectly.
Thanks so much Phil,