What a bummer! That happened with me, too, with the most recent dogs we adopted; our livestock guardian dog went missing for 4 days before we found him and our little Chihuahua Rat Terrier mix backed out of her (new) collar and bolted! (Thankfully we got them both back.)
I hope you have some good neighbors that can be on the lookout and you eventually find them! If you use Craigslist, I would maybe try posting there as well and if you have one, possibly letting the humane society know you are looking for them.
I'm hoping the best for them! Welcome to BackYard Chickens!