Do Jehovah's witnesses believe that Jesus appeared in the Old Testament? Many Christian teachers as far back as the early church fathers have taught it was Jesus that appeared to Abraham before destroying Sodom and Gammorah, wrestled with Jacob in the dessert, and appeared at other times in the Old Testament scriptures. 

Do Jehovah's whitnesses also teach that Jesus appeared to some people before his incarnation?
Beyond the general belief related to the Archangel Michael, Jehovah's Witnesses do believe that Jesus makes an appearance in the Old Testament. 

Under the article "The Word" in the JW reference work Insight on the Scriptures Vol. II page 1203 it says this: "In a similar way God’s firstborn Son doubtless served as the Mouth, or Spokesman, for his Father, the great King of Eternity. He was God’s Word of communication for conveying information and instructions to the Creator’s other spirit and human sons. It is reasonable to think that prior to Jesus’ coming to earth, on many of the occasions when God communicated with humans he used the Word as his angelic mouthpiece."

Citing a number of scriptural citations, the article assumes that Jesus was the angel that: stopped Abraham from sacrificing Isaac; spoke to Moses through the burning bush; may have been the angel that was charged with leading the nation of Israel through the wilderness. In all except the latter case, the scriptures referenced specifically mention "Jehovah's angel." 

So the Jehovah's Witnesses belief that Jesus appears in the OT is primarily based on Jesus identity as "The Word" as well as the OT wording "Jehovah's angel."