Perhaps the mother is not feeding him because of his age. When squeakers get to 3-4 weeks of age, parents usually stop feeding them, and they need to ba able to fend for themselves then, or else they need a little help from us. The other possibility is that parents do not feed youngsters who are very sick, but surely that isn't the case...?
As for Pablum I had no idea what that was, so I had to google it. It seems like a good idea, if you're not able to obtain hand raising formula for him, but please note that the vitamin D it contains will not be absorbed by the bird, it's only for humans. Homie will need vitamin supplements suitable for pigeons, and especially Calcium with Vitamin D3 if he's getting no direct sunlight.
Are the feathers on his face and neck growing yet?