1 John 1:1 - That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon, and our hands have handled, concerning the Word of life 2 the life was manifested, and we have seen, and bear witness, and declare to you that eternal life which was with the Father and was manifested to us 3 that which we have seen and heard we declare to you, that you also may have fellowship with us; and truly our fellowship is with the Father and with His Son Jesus Christ.
1 John 2:1 - My little children, these things I write to you, so that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous.
1 John 3:1 - Behold what manner of love the Father has bestowed on us, that we should be called children of God! Therefore the world does not know us, because it did not know Him. 2 Beloved, now we are children of God; and it has not yet been revealed what we shall be, but we know that when He is revealed, we shall be like Him, for we shall see Him as He is.
It clearly sounds like 1 John is written to Christians to me. I'm yet to find a NT book that is written directly to non-Christians, although just because a letter in the NT is written TO Christians does not means that everyone being discussed in the letter IS a genuine Christian.