Here's a simple idea to encourage people to commit to praying for specific people who don't know Jesus.

Say:
"God wants us to reflect him and his glory to all those around us. Let's commit to praying for one specific person this week. Let's pray that as we keep close to God, he will be reflected in all that we say and do. And, that as we are gradually transformed into his likeness, our every moment will become a reflection of who he is."

Then read and/or project 2 Corinthians 3:18 (New International Version):

"And we, who with unveiled faces all reflect the Lord's glory, are being transformed into his likeness with ever-increasing glory, which comes from the Lord, who is the Spirit."

Next, encourage the group to come and write the name of the person they commit to pray for this week, onto the mirror. Explain that this is a symbol of their desire to be the reflection of God to those around them.