1) Where does it say that the 144,000 are evangelists?
2) If the Great Commission is accomplished by angels, then why are there people from every tribe language and nation coming out of the Great Tribulation (Revelation 7), long before the angel makes the announcement in Revelation 14?
9 After this I looked, and behold, a great multitude that no one could number, from every nation, from all tribes and peoples and languages, standing before the throne and before the Lamb, clothed in white robes, with palm branches in their hands, 10 and crying out with a loud voice, “Salvation belongs to our God who sits on the throne, and to the Lamb!” (Revelation 7:9-10)
3) When Jesus gave his commission to preach his death and resurrection to "all nations," do you think he meant his followers, or an angel?
45 Then he opened their minds to understand the Scriptures, 46 and said to them, “Thus it is written, that the Christ should suffer and on the third day rise from the dead, 47 and that repentance for the forgiveness of sins should be proclaimed in his name to all nations, beginning from Jerusalem. 48 You are witnesses of these things. (Luke 24:45-47)
To the Galilean Disciples:
John 15:26-27 But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of Me:
And ye also shall bear witness, because ye have been with Me from the beginning.
"From the beginning" meaning these guys here:
Matthew 10:2-7 Now the names of The Twelve Apostles are these: The first, Simon who is called Peter, and Andrew his brother; James the son of Zebedee, and John his brother; Philip and Bartholomew, Thomas and Matthew the publican; James the son of Alphaeus, and Lebbaeus whose surname was Thaddaeus; Simon the Canaanite and Judas Iscariot, who also betrayed Him. These twelve Jesus sent forth, and commanded them, saying, Go not into the way of the Gentiles, and into any city of the Samaritans enter ye not: But go rather to the Lost Sheep of the House of Israel. And as ye go, preach, saying, The Kingdom of Heaven is at hand.
...and here:
Matthew 28:16-20 Then the Eleven Disciples went away into Galilee, into a mountain where Jesus had appointed them. And when they saw Him, they worshipped Him: but some doubted. And Jesus came and spake unto them, saying, All power is given unto Me in Heaven and in earth. Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
Teaching them to observe all things whatsoever I have Commanded you: and, lo, I am with you alway, even unto the end of the world. Amen.
Revelation 7:9-10 is a flash-forward of Revelation 15:2-3.
Revelation 11:12 And they heard a great voice from Heaven saying unto them, Come up hither. And they ascended up to Heaven in a cloud, and
their enemies beheld them.
Their enemies is the remnant in Jerusalem, who will go on to teach the same thing Jesus taught His Lost Sheep of the House of Israel... to the multitudes on the glass sea.
The Gospel of the Kingdom:
Matthew 26:13 Verily I say unto you, Wheresoever this Gospel shall be preached in the whole world, there shall also this, that this woman hath done, be told for a memorial of her.
That makes the Gospel of the Kingdom none other than the Four Gospels themselves... two of which are first-hand witnesses of Jesus.