How do you search groups on facebook?

[S©O®P1AN]

[Yuuuup]

When you start typing something into the search bar at the top of Facebook, the most relevant results start showing in the typeahead. If you see what you're looking for in the typeahead, click on it to save time searching. If you don't see what you're looking for, click See more results at the bottom for a full list of results.

[Dmitry N]

I'd suggest you to try special site listed below, it allows to make keyword search around facebook without logging in, so you may narrow down your search results with any criterias like "group" + interests etc. Check up link below.
Good Luck)