I haven't anything helpful to suggest, but have been exploring the kinds of places I look for these kinds of things. Hopefully these links work: Goodreads list of Young Adult books about/with Angels, and a tagmash in LibraryThing for angels, series, young adult. May your book(s) be there!

The comments for the Goodreads list suggest it is a bit of a mess -- not everything is YA, not everything is angels, some are duplicates. The tagmash might not be quite right -- maybe try other options? (I tried Scholastic, angels, series and only got a few, none of which looked very helpful).