Paul, Apostle of Jesus, wrote: "Let no man beguile you of your reward in a voluntary humility and worshipping of angels, intruding into those things which he hath not seen, vainly puffed up by his fleshly mind," (Colossians 2:18)
And yes, that's what asking Michael the Archangel for help is - an example of worshipping of angels. We are nowhere encouraged to trust in angels for deliverance. Instead, our trust is to be in God. We should ask God for deliverance, not Michael the Archangel.
In case you think there is some ambiguity in the tweet, and that the pontiff could be just asking God to send Michael - consider these more complete remarks (from two and a half years earlier), "In consecrating Vatican City State to St. Michael the Archangel, I ask him to defend us from the evil one and banish him." (link)
Michael wasn't the only worshiped creature at that particular consecreation:
We also consecrate Vatican City State in St. Joseph, guardian of Jesus, the guardian of the Holy Family. May his presence make us stronger and more courageous in making space for God in our lives to always defeat evil with good. We ask Him to protect, take care of us, so that a life of grace grows stronger in each of us every day.(same source)