Identify potential ministers within your congregation or from the people around you. Look for people who have the gift of public speaking and those who command the attention of whomever they are speaking to, regardless of the topic. Look out also for people with an interest in ministry. Such people tend to make powerful evangelists.
Explain the importance of ministry to your students. Point out the need to be steadfast in the word of God and to draw others to it. Use biblical references, such as the story of Noah's ark, to drive the point home.
Study the book of Acts together with your students to help them understand the three key goals of evangelism: conversion, proclamation and community. The book of Acts speaks of the endeavors of the apostles to preach the gospel and the ups and downs that came with the ministry.
Hold Bible study sessions regularly with your students. Teach them how to interpret various scriptures in the Bible. An evangelist needs to have in-depth knowledge of the Bible so as to effectively carry out his duties. He cannot preach on a topic he is not conversant with.
Encourage your students to practice what you teach them. Take them with you when you go for fellowships or events where you are invited to preach. Encourage them to come up and preach alongside you. Keep doing this until they build up the confidence needed to preach on their own.
Inculcate a habit of prayer in your students. Regularly hold prayer meetings with them and show them how to pray. Teach them how to pray both for themselves as they carry out their mission as well as intercede for others.