Since it seems it's not yet done, my advice for you going forward depends on what you want the search engine to do. If you just want it to search a limited amount of data (say, a user registry on your site),
MySQL is definitely the way to go. It makes creating custom searches almost too easy, and it's a simple technology to learn.
If you want to search a large amount of data (like the internet), however, a MySQL database probably won't meet your needs, because it will become enormous and cumbersome. For that, you should know that Google (and, I assume, other major search engines) uses a spider that traverses the desired data and creates a index thereof. I have no idea how a single user could afford the hardware necessary to store and quickly search so much data.