Objection 1. It would seem that the demons will not carry out the sentence of the Judge on the damned after the day of judgment. For, according to the Apostle (1 Corinthians 15:24): "He will then bring to naught [Vulgate: 'When He shall have brought to naught', etc.] all principality, and power, and virtue." Therefore all supremacy will cease then. But the carrying out of the Judge's sentence implies some kind of supremacy. Therefore after the judgment day the demons will not carry out the Judge's sentence.
Objection 2. Further, the demons sinned more grievously than men. Therefore it is not just that men should be tortured by demons.
Objection 3. Further, just as the demons suggest evil things to men, so good angels suggest good things. Now it will not be the duty of the good angels to reward the good, but this will be done by God, immediately by Himself. Therefore neither will it be the duty of the demons to punish the wicked.
On the contrary, Sinners have subjected themselves to the devil by sinning. Therefore it is just that they should be subjected to him in their punishments, and punished by him as it were.
I answer that, The Master in the text of Sentent. iv, D, 47 mentions two opinions on this question, both of which seem consistent with Divine justice, because it is just for man to be subjected to the devil for having sinned, and yet it is unjust for the demon to be over him. Accordingly the opinion which holds that after the judgment day the demons will not be placed over men to punish them, regards the order of Divine justice on the part of the demons punishing; while the contrary opinion regards the order of Divine justice on the part of the men punished.
Which of these opinions is nearer the truth we cannot know for certain. Yet I think it truer to say that just as, among the saved, order will be observed so that some will be enlightened and perfected by others (because all the orders of the heavenly hierarchies will continue for ever) [Cf. I, 108, 7,8], so, too, will order be observed in punishments, men being punished by demons, lest the Divine order, whereby the angels are placed between the human nature and the Divine, be entirely set aside. Wherefore just as the Divine illuminations are conveyed to men by the good angels, so too the demons execute the Divine justice on the wicked. Nor does this in any way diminish the punishment of the demons, since even in torturing others they are themselves tortured, because then the fellowship of the unhappy will not lessen but will increase unhappiness.
Reply to Objection 1. The supremacy which, it is declared, will be brought to nought by Christ in the time to come must be taken in the sense of the supremacy which is in keeping with the state of this world: wherein men are placed over men, angels over men, angels over angels, demons over demons, and demons over men; in every case so as either to lead towards the end or to lead astray from the end. But then when all things will have attained to that end there will be no supremacy to lead astray from the end or to lead to it, but only that which maintains in the end, good or evil.
Reply to Objection 2. Although the demerit of the demons does not require that they be placed over men, since they made men subject to them unjustly, yet this is required by the order of their nature in relation to human nature: since "natural goods remain in them unimpaired" as Dionysius says (Div. Nom. iv).
Reply to Objection 3. The good angels are not the cause of the principal reward in the elect, because all receive this immediately from God. Nevertheless the angels are the cause of certain accidental rewards in men, in so far as the higher angels enlighten those beneath them, both angels and men, concerning certain hidden things of God, which do not belong to the essence of beatitude. In like manner the damned will receive their principal punishment immediately from God, namely the everlasting banishment from the Divine vision: but there is no reason why the demons should not torture men with other sensible punishments. There is, however, this difference: that merit exalts, whereas sin debases. Wherefore since the angelic nature is higher than the human, some on account of the excellence of their merit will be so far exalted as to be raised above the angels both in nature and rewards [Cf. I, 108, 8], so that some angels will be enlightened by some men. On the other hand, no human sinners will, on account of a certain degree of virtue, attain to the eminence that attaches to the nature of the demons.
Source: Summa Theologica (New Advent)