Hi Sir or Madam,
It is very important for small dogs to eat on a very regular basis as they can quickly become hypoglycemic leading to seizures and serious health issues. I'm going to talk first about trembling.
Shaking or trembling in toy breeds could be due to hypoglycemia, liver shunt, or a neurologic response such as a seizure. Trembling can also be a sign of pain, stress and cold.
Hypoglycemia is low blood sugar and frequently causing trembling in small breeds. Feeding your dog smaller meals more frequently can help. If you suspect your dog is having low blood sugar you can put a drop of pancake syrup on your dog's tongue which should raise the level. Since your dog isn't eating that may have caused the trembling.
A liver shunt is usually a genetic condition. It is a condition where instead of the blood going through the liver and being cleansed, part of the blood is diverted around the liver resulting in a toxic buildup in the blood. These are commonly seen in yorkies. You can read about these here: http://www.malteseonly.com/shunt2.html
Seizures can manifest as trembling and a dog may not lose conscienceness. You can read more about seizures here: http://www.marvistavet.com/html/body_seizure_disorder.html
So if he is not eating that may lead to vomiting of stomach acids due to having an upset stomachand lead to hypoglycemia, so definitely get some karo or pancake syrup on his tongue to prevent hypoglycemia.
You will wnat to check his teeth and see if there is any darkened teeth, tartar buildup, broken teeth or red gums indicating irritation. A tooth issue can cause a dog to not want to eat. If you find any, buffered aspirin can be given to a dog with a dosage of up to 5 mg per pound every 12 hours for pain until your dog can be seen by your Vet. Keep in mind that a dog's body does not metabolize aspirin in the same way as a human and thus should not be given more than a day or two without contacting your Vet.
If this isn't a tooth issue and he has had a bowel movement recently, then it might be a stomach ache perhaps from an unusual treat or from something he ate. You can give your dog some pepcid or Zantac. Read about Pepcid dosages and usage information here: http://www.petplace.com/drug-library/famotidine-pepcid/page1.aspx
Zantac can be given to a dog at .25 to 1mg per pound every 8-12 hours. Read about usage here:
I'd start feeding your dog smaller meals 4 times a day taking up the food bowl afterwards. This way your dog will have food in its belly on a regular basis throughout the day. This will cut down on excess bile. I'd also add a spoonful of plain yogurt to your dog's food 2-3 times a week to add good bacteria to your dog's stomach to aid in digestion as well. The bland diet of boiled chicken and rice can be used for a few days. If your dog does fine, you can slowly reintroduce your dog's regular food into the chicken and rice mixture until it is all regular food.
If your dog has not had a bowel movement recently then you may be looking at constipation or an intestinal obstruction. You can read about these things below.
If she has had an unusual treat such as bacon, ham, or fried or fatty foods, that may have triggered a touch of pancreatitis. We would recommend witholding food for 6-12 hours and then offer small portions of bland food. However, you will need to be sure she doesn't become hypogycemic, so add some sugar to the water or get some nutrical from your pet store to be sure he is getting some nutrition.
If these things do not work for your dog, then your dog will need to go to the vet and have tests run to determine if a more serious condition is present. I hope this information is helpful to you.