Even though Photos for iOS doesn't offer a Faces album, you can still find tagged friends using the search field.
I recently wrote a post on getting Faces to sync between multiple computers when you're using iCloud Photo Library, and mentioned — sadly — that there was no efficient way to sync the work-around to iOS. And this remains true... technically.
It turns out that even though Apple doesn't officially sync the Faces album from Photos for OS X using iCloud Photo Library, you can still find any tagged photos of a person — no matter what computer you tagged them on — by searching their name.
How to search your iPhone, iPad, or Mac for Faces and Places
- Open Photos for iOS on your iPhone or iPad, or Photos for OS X on your Mac.
- On iOS, tap the Search icon. On OS X, click on the Search field in the upper right corner.
- Enter "[person name]" to find the tagged face in question.
Big thanks to commenter atlwx for pointing out this awesome tip.