You cannot really find an instance in the New Testament of anyone who came to faith apart from another person's involvement. Although there are exceptions, this is how most people become Christians.
Take for example, the Philippian jailer, whose conversion is recorded in Acts 16. God could have reached him in many ways, but He chose to use Paul and Silas, whom he allowed to be imprisoned for preaching the gospel. They were mistreated by this jailer, but when an earthquake struck and the jailer faced execution because the prisoners would have gone free, Paul and the others chose to stay in the prison. The jailer asked, "Sirs, what must I do to be saved?" (Acts 16:30), and the Bible tells us that not only did the jailer come to faith, but so did his entire household.
Another example is found in the story of Cornelius, a centurion in the Italian Regiment who had a heart to know God. An angel appeared to him and told him he needed to talk to a guy named Simon Peter, who was in Joppa. So Cornelius sent for Peter, and Peter shared the gospel with Cornelius.
Even Saul of Tarsus, whom we know as Paul, was converted on the Damascus Road, having a direct encounter with Jesus. Yet he had his heart opened and softened through the testimony of young Stephen, the first martyr of the church who prayed as he was dying, "Lord, do not charge them with this sin" (Acts 7:60).
Yes, God uses people to reach people, but God is the one who saves them—not us. This seems rather obvious, but sometimes we forget it. God will prepare a person's heart to hear and receive the gospel. He uses us, but He is the one who does the work.