Needless to say, there is NO SCRIPTURE that they can point to. Instead, they use alot of presumption and tortured reasoning to arrive at their conclusions. They will use primarily the Scripture in 1 Thess. 4:16, where it says....
"For the Lord Himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:"
From this verse, they say that Christ will shout with the archangel's voice, so therefore, He must be the archangel. There are a number of things to point out here....
First, it does not say that Jesus is the One Who is doing the shouting. It says He will descend WITH a shout. The word "with" means "accompanied by". For example...."I went to the store WITH my wife." Does that mean that I am the same person as my wife? No. It means that she accompanied me to the store. In fact, there are some verses that clearly say that, when Jesus comes, all of the angels will be coming WITH Him.
Check out the following verses: Matthew 25:31, Mark 8:38. It makes sense that the arrival and coming of a King would be announced by a loyal subject, which in this case, will be Michael the Archangel. There will be a shout from Michael, and then the blowing of the trumpet to announce the King's arrival in the rapture.
Suffice it to say, there is nothing in 1 Thess. 4:16 that states that Michael and Jesus are the same Person.
Secondly, the JWs only seem to read the part of 1 Thess. 4:16 that suits their purpose. If we read the whole verse, and apply their logic, then we have proof that Jesus is also God, for the very next statement says that Jesus comes "WITH THE TRUMP OF GOD". Now, if we use JW reasoning, and say that Jesus' coming WITH the voice of the archangel means that He IS the archangel, then we must also conclude that Jesus' coming WITH the trump of God means that He is God. Of course, JWs would strongly disagree, but if their logic is to be used, then they must be consistent and interpret the whole verse the same way.
Of course, it is plain that both the voice of the archangel and the blowing of the trumpet are simply announcements of Christ's coming, and neither are done by Christ Himself.
Also, the JWs make some strange connections from the book of Revelation, primarily chapter 12, where Michael is said to have angels under His command.
"And there was war in heaven: Michael and HIS ANGELS fought against the dragon; and the dragon fought and his angels:"
Then, the JWs find other verses that say that Jesus has angels under His command, and arrive at the conclusion that, because they both are said to have angels under their command, then they must be the same Person. I am sure that you can see the ridiculous nature of that logic. A military commander may have soldiers under his command, and he can rightly call them "his soldiers". However, the President of the United States is the "Commander in Chief" of the military, and therefore, he can also refer to them as "his soldiers". This does NOT mean that the military commander and the President are the same individual.
I believe any sane person can see the shallow nature of the Watchtower reasoning. The fact is: THEY DO NOT HAVE ONE SINGLE SCRIPTURE THAT THEY CAN POINT TO, SAYING CLEARLY THAT JESUS CHRIST IS MICHAEL. Do not let the JWs get away from this fact, but press them on it.