The poem goes:

One ring to rule them all. One ring to find them. One ring to bring them all. And in the darkness bind them.

In what way does the one ring find anything? Do we have some reference, besides this poem, that Sauron could use the ring to know where all other ring wearers were?

The other 3 lines seem true. The one ring was about control and certainly had the ability to rule and control other ring wearers. But, not sure about finding them.