Text: John 14: 12 (ESV)
“Truly, truly, I say to you, whoever believes in me will also do the works that I do; and greater works than these will he do, because I am going to the Father.
The favourite phrase of Jesus: "truly, truly, I say to you ... " (which occurs often but only in the Gospel of John, first in John 1:51) is directed to the person or people to whom Jesus is speaking at the time.
Thus, Jesus comments are literally directed to the disciples or the crown, depending on the context. However, since nothing that Jesus said was ever confined only to those to whom He spoke but was recorded for all posterity, by simple and legitimate extrapolation, anything that Jesus said, is directed to all people of all time who are willing to "hear" what Jesus said.
Concerning this formula, Ellicott (in comments about John 1:51) says:
They are always spoken by our Lord, and connected with some deeper truth, to which they direct attention. They represent, in a reduplicated form, the Hebrew “Amen,” which is common in the Old Testament as an adverb, and twice occurs doubled (Numbers 5:22; Nehemiah 8:6). In the Hebraic style of the Apocalypse the word is a proper name of “the faithful and true witness” (Revelation 3:14).,
Barnes makes a similar comment:
Verily, verily - In the Greek, "Amen, amen." The word "amen" means "truly, certainly, so be it" - from the Hebrew verb to confirm, to establish, to be true. It is often used in this gospel. When repeated it expresses the speaker's sense of the importance of what he is saying, and the "certainty" that it is as he affirms.
Since Jesus prefaced some His remarks with this phrase, it is these very teachings which follow to which all Christians must pay particular attention because of their deeper and more important content.
Exegetically, the pronoun "you" (2nd person plural, in the phrase "I say to you") referred solely to the disciples who were with the Lord following the Last Supper in chapter 13.
Your question should be whether the pronoun "he" or "whoever" (nominative masculine singular, in "ho pisteuon") refers to all believers or only to some believers.
Whatever the application is, logically the promise cannot apply to all believers, because some believers die or become incapacitated soon after they come to saving faith (one thinks of the thief on the cross who accepted Jesus as Lord while dying). Others who are undoubtedly saved will die at a young age, or isolated (in prison), or incapacitated (through paralysis or medical infirmity) and have no real opportunity to perform "works" or "greater works", whatever one supposes those works to be.
The "you" refers to the believers that are CALLED by Christ to serve as apostles. These apostles include the first twelve set of apostles chosen by Christ, and others that will be added later to serve as apostles.
Christ made that statement in reference to the Holy Spirit which he will send to his called apostles when he goes to the Father.
Not all believers are called to serve as apostles; just as not all children of God are called to serve as a religious leader.
Acts 1:8 But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.
The Holy Spirit is prove for the apostles to act as witnesses unto Christ by the miracles ("will also do the works that I do; and greater works than these will he do") they shall perform. This prove which is the Holy Spirit shows that Christ fulfilled his promise that he will send the Holy Spirit when he goes to the Father in heaven, and also proves that he rose from death.