Yeah, Im more a dog expert, But that little guy isn't old enough to be entirely on solids. Milk formula will be the best substitute for breast milk, You will want to feed it through a syringe or off a teaspoon. Its a 24/7 job though, So if you have someone else who can take "Shifts" looking after it (I breed toy dogs, They need to have someone watching all the time for the first week.)

Kitten Milk Replacement. http://www.walmart.com/ip/KMR-Kitten...ndingMethod=rr
You can find it at PetSmart/Petco too. (NO cow milk, it causes diarrhea in kittens which leads to rapid dehydration in one that small)
Keep the kitten away from your other pets, especially any other cats, as it could be carrying FIV, FIP and you don't want that nightmare. Keep it in a small room to reduce stress with a litter box, a blanket and a watch or wind up clock underneath the blanket. Mimics the sound of a heartbeat.
Vet visit is a must. If you can't keep the kitten, find a no kill shelter in your area. If you need help finding one, contact me. Thanks for being so kind to a kitty in need

He looks really young. Try some milk formula with a syringe. Also lots of blankets, maybe a stuffed animal and love from you

For a kitten that small, you should get it some formula. A thing to keep in mind is, it might not be able to eat kitten food yet. This might be the case if it seems uninterested in the food. Your best best is formula for now I'd say, and to take it to a vet to have him/her checked out.

Also, get it a small stuffed toy to sleep with the keep it warm at night. Really tiny kittens usually have the warmth of their brothers and sisters at night.

Aww, its so cute. It is nice to see such a display of compassion too. Give it formula as recommended by others, it definitely can't handle solid food yet and wont be interested in wet food either.

I used to feed kittens a mixture of warm milk and an egg. I put it in a syringe and injected it in their mouth. Makes them fat.

Dawwwwwwwwwwww....

KATARINA! It's destiny. Her name is Katarina. You gotta do it! You looked for help on the LoL forums, it only makes sense!