[UPDATE] Found him! He's fine, my brother feels much better, thanks for all of you that gave suggestions. <3

So a little bit about the situation, my brother saved a rabbit that was wandering around the neighborhood (he used to breed them, just put his oldest girl down due to cancer, he was heart broken over her, he cares, now he's freaking out), and now he's incredibly concerned about this new little guy, Jasper. <3

We live in Washington state, so due to the cold weather, he brought his other bun, Hop-hop, in and also the new rabbit, Jasper in. He and I have both seen him today. I had to do laundry, so he kind of skitted off (still skittish, new place, we get that), then my bro and I went to run errands, came home, had to do some stuff downstairs, my brother saw him, and then went to look for him later, and we can't find him anywhere downstairs and there are TONS of places he could be hiding, he's been looking for Jasper for a few hours now and my brother is freaking out, understandably.

To add, Jasper has been in the basement for almost two weeks now, along with Hop-hop, and Hops really seems to like him, he's been eating, drinking, using the litter box, so he seems like he's been adjusting, but we have no idea where he is, so hope you all can help.

Do you all have any tricks or tips on how we can find him? Where might be a good place to look? TIA. <3