First, I wouldn't assume that your pup is missing his mother. Puppies cry for different reasons and one might be that he is not well. Have you checked with your vet?
Assuming that your pup is well, here are some things that have worked for me:
1. The best thing is to have the pup sleep in your bedroom.
2. Soft radio.
3. Ticking clock within hearing range.
4. Hot water bottle under the pup's blanket.
I hope your pup is doing better soon, Jan