Not usually. This is probably alopecia and should probably be evaluated by a veterinarian. Sometimes hair loss is nothing more than the dog having a chronically itchy spot, but sometimes it is a sign of a major disease.
It's getting old. Give it vitamins.
teacup Yorkies do have human hair
All dogs have hair, but if you mean LONG hair, only if the chihuahua was the long haired breed.
Chihuahua Short Hair
Take him to the vet He could have a serious skin condition starting.
I would think that if you are losing hair, its not because of what your eating though. But you could eat things with fiber in it.
I have a three month old teacup poodle too and she has thinner hair than my miniature/standard poodle has. The back of her legs are very thin and I can see her skin. Not sure if all teacup are like this or not, this is our first teacup.
The Short (Smooth) haired Chihuahua would shed less fur, the long haired would need more grooming suggesting that the long haired would shed more (there's more hair)
If it's a male, he would not have balls; female - there would be a scar, but hard to find.
Chihuahua
If a dog (any dog) is losing hair in big enough patches to see his bare skin where he has lost it, he probably has mange, and should be seen by a vet. There are other causes too,but mange is the first thing the vet will suspect. Take him to the vet.
It kepps you from losing your hair most of the time but some side effect are losing of hair.