Yes, you need to force feed. I HIGHLY recommend Against using a pinky. They are much harder to digest, especially for a weakened frog. It is hard to tell exactly from the photos, but he seems small. Try force feeding earth worms, like Jessica said. They are much easier to swallow and digest; they will get nutrients absorbed into his body faster. In his weakened state, it would even be possible for your frog to choke to death on a pinky especially if he is small. (Gerneral rule of thumb is not to give a pinky to a frog less than 2 inches STV.)

Here is how to force feed: Take him out of the enclosure and set him on some damp paper towels (moistened with de-chlorinated water). It is easier to do if you have two people: one to hold the frog steady and the other to open his mouth and insert the food. Gently cup the frog from behind to keep him from backing away. The other person uses a credit card or shopper card to pry his mouth open. (I prefer the shopper cards because they are smaller but still firm.) Insert the card on one side of the mouth (it should be about where his stripe comes down his nose). Gently but firmly press down, increase the pressure until he opens. You should have the food item ready in your other hand and pressed against his "lips" so that as soon as he opens you can stick it in his mouth. You don't have to get the entire item in his mouth. Once food is partially swallowed, their instinct will usually take over and they will swallow it the rest of the way. He will try to swat away the card and the food. It will take several tries to get the food in his mouth. It is best to use worms. Dust the worms with a vitamin supplement. Worms are much easier to digest. Anytime an animal goes long periods without eating, their stomach shrinks, so soft smaller food items are better. Bigger items or items with shells, exoskeletons, or bones are harder to swallow and require much more energy to digest. Your frog does not have any extra energy. He needs nutrients immediately. If you can, pick up Flucker's Repta Aid. It is an emergency aid supplement that works very well. It comes with a tube syringe that you squirt the supplement into the frogs mouth. You can also use cat food. I know that sounds weird, but it is what the vet prescribed when my pac Grif wasn't eating. It was a high protein cat food used for emaciated animals or ones recovering from surgery. It is much easier for them to digest. You use a tube syringe, follow the same force feeding method, and squirt the food into the frog's mouth. It gets the vital nutrients in an easy to digest form. Just make sure you get one without chunks (they will clog up the syringe). I cannot emphasize enough how critical it is to take immediate action. Judging from the photos, your frog may not have long to live. I do not mean to sound harsh, but his life is in danger. Please keep us posted.