One might expect the explorer and the radio room to work together to bring new dwellers, alas they do not.
A dweller exploring the wasteland does one thing: explore the wasteland to find weapons, outfits and CAPS. S/he doesn't recruit anyone for the vault.
A dweller working the radio room does one thing: transmit a radio signal in the hope of attracting a new dweller. Click on the radio room and you'll see a timer. When that timer elapses, FOS calculates the probability that someone in the wasteland heard the call, based on the size of the radio room and the sum charisma of its dwellers (including outfits).
If you've tried to adjust the time on your device to trick the game, all explorers in or sent to wasteland will encounter nothing until the game catches up to the time adjustment you made.
In short, if you've changed time settings on your device, expect to find nothing, and get zero updates from the wasteland for however long you adjusted the time.
If you changed the time for many days, you will have to wait for that many real world actual days before the wasteland will work again.
If all you've done is cross a time zone from taking an airplane somewhere, then, you will only have to wait however many hours the time zones you've crossed have adjusted your device time compared to how the game responds to changes made to the time on the device.
If you try to cheat the game by adjusting time, it has consequences.
If all you have is just one explorer in the wasteland, you probably just started playing. Before the update, many folks had 50 - 75 explorers out in the wasteland for 3 or 4 days exploring and than taking a day or 2 to return.
You could try starting a whole new second vault to see if the same thing happens there when you send out a dweller.
With the recent 1.2 update, it might take hours, or even a whole day for any wasteland explorer to find any items, but, you should at least get update messages on the wasteland screen that shows your explorer is fighting wasteland enemies and other things.