Pocket Frogs currently uses Game Center for friends and automatically populates your neighbors with your current Game Center friends who also play Pocket Frogs.
With iOs 10, Apple has removed the ability to edit your Game Center friends list. We are working on an update to address this issue and a few others. Unfortunately we've have run into some major issues along the way which has slowed the progress. We don't have an ETA on the update but we are still working on it.