Thread Filter by AddonsLab - this plugin allows you to filter and search for topics based on additional fields. The idea is to allow administrators to use the capabilities of additional user fields to turn their forums into a Catalog, Ads, Store, or other types of content for which filtering data based on user fields is vital.

Info:

Controls for filtering streams are added in the Filters pop-up window in the list of streams. Each field can be configured separately so that it appears in the filter list and/or in the search form.

Text fields are searched and indexed in the same way as the text of the stream itself. The full-text search is performed with a fuzzy match, that is, the search phrase does not have to be in the same order as in the query.