I had the same problem, I got my pup when she was 10 weeks. She was the runt, and wasn't socialized by mom enough to learn to eat on her own. The breeders were feeding her from a jar lid, and since I had a litter of Mini Scnhauzer pups before, they said I could take her at that age. Hand feeding wasn't working well at my house, she would eat from a spoon, but not well. After she didn't eat for about 12 hrs, her blood sugar dropped and we had to go to the vet.
Anyhow, the vet said to use a syringe to feed her. They gave me one told me/ showed me how to water the food down and said to give her 4 to 5 ml every 4 hrs., along with .5 ml of karo syrup ( to keep her blood sugar up). I kept increasing the amount by 2 ml every 4 to 7 days if she seemed hungry before the time of the next feeding. At around 6 mo. she started eating some food on her own from a glad storage lid.
I still put about 1 tbls of kyro syrup in her water dish, just to keep her blood sugar up.
To feed her, I use 1 to 2 tablesppons of ground up Chicken Soup for the Puppy Lovers Soul in the lid, wet down with the water mix, and about 1 to 2 tablespoon of smashed up merricks canned food. ( The canned food I smashed up because the meat chunks were too big.) I also added water mix to the canned to make it like thick pancake mix. She liked it, but she wasn't ready to commit so I had to watch her, and if she didn't eat what was offered within 30 to 45 mins, I'd syringe feed her.
If she did eat on her own, I praised her and made a Huge deal out of it. It's taken awhile to get her here, but she's eating on her own finally. She's 7 mo.
Yorkiemom1 was a huge help when I was 1st going through this. The best thing she told me was to remember that my pup was too young to be taken from her mom, and I was now the mom. She also suggested using nutri-cal- a tube of vitamin rich paste- and Holistic Health Extension " Little Bites" for puppies... My girl eats this between meals like a snack, usually from my hand. Also, yorkiemom suggested getting nutra drops, a vitamin syrup that promotes eating (the little bites are coated in it). I used this in a syringe with the karo surup, like about .5 ml of each in the same syringe. Gradually I increased the amounts of both to 1.5 ml of each. She doesn't get those now, but if she seems sluggish ( like she was when her blood sugar was low) I give her some and she's fine.
Another helpful thing was getting samples from dog food companies. My girl is a fussy eater, and the samples saved me a ton of money. I didn't have to buy 10 lbs of food to find out she didn't like it
And my neighbors dog now loves me too, because whatever mine didn't like, he got! LOL!
If you have any other questions, message me. I'm sure Yorkiemom would help you too if you have other questions.