Worried sick about a recently adopted foster cat

I'm so worried about my foster cat that I just don't know what to do. I don't think I'm going to be able to sleep tonight over this. Hopefully I'm overreacting.

This boy, AJ, has been with me since he was a kitten and was adopted last Thursday by a nice young family that seemed very excited to adopt him. They emailed me on Friday night telling me that he was doing fine and warming up to them. I emailed them back on Saturday and asked them a few questions but I didn't hear back. Before they adopted him they responded to emails very quickly. I waited and sent them a second email late Monday night and not it's Wednesday night and I still haven't heard back. So I decided to call them and dialed their home number. The number had been turned off. I called their cell phone and it went directly to voice mail. I haven't called them before so I don't know how long their home phone has been turned off.
I'm getting so nervous that something is wrong. Why wouldn't they respond to me? My fear is that AJ has got out of the house and they are afraid to talk to me. If that's the case he's been gone for days now. I just feel like crying. I just can't figure out why they wouldn't respond to my emails.

If I haven't heard from them by tomorrow afternoon I'm driving up there. Please pray for AJ that he's okay and safe and sound.

I can understand if they don't want to have contact with me but I don't understand why they can't drop me a line to let me know if he's still terrified and what his new name is. I've had him for a year and a half since he was a tiny baby and I just want to know that he's okay and is not still sitting under the dresser shaking like he was when I dropped him off. We talked about this when I dropped him off, that I would really appreciate if they would let me know how things goes in the beginning and I never got the idea that they had an issue with that. Had they just responded to my first email, which I think is common courtesy, I certainly would not have contacted them again. When they didn't respond to me I was afraid that he had got out and maybe they were embarrassed to tell me. I don't see why they would be annoyed. All they had to do is write me one sentence after I asked a couple of general questions when I responded to their email. I don't think it's out of line to expect that at all. Just ignoring someone is rude. I've done many adoptions and have never run into this issue. All I expected was for them to respond to one email. I only started to contact them several times after they failed to do that for three days.
I'm the foster parent and the adoption coordinator and all adopters sign a contract agreeing to being checked on so we can ensure the cat's welfare. That's explained to them before adoption.

I finally did manage to get in touch with them today though. I friended the girl on Facebook and she responded to that. She says that AJ is doing fine and I can just hope that's the truth.

I finally chatted with the adopter on Facebook and even got some pictures so now I'm feeling much better. He really looks happy in the pictures and he sounds like he's doing great. I even got a picture of AJ with their 3-year old who he was really scared of at first. Now he sleeps on her bed. Go figure!
It's good to know that he isn't lost out on the street, hit by a car or some other horrible fate that I've been imagining. I'm really silly like that. If my husband comes home a half hour late I'm sure he's laying in a ditch somewhere.

I'm always really happy when one of my fosters get adopted but it is bittersweet. Especially like with AJ who's been with me for so long. After a year and a half they're like one of my own and I always worry that they are afraid or unhappy after I leave them, just like I am if I have to leave one of my own guys somewhere. But now that I know that he's no longer terrified and seems happy I feel much better about the situation.