Here's a quick idea to help youth share their faith.  It's really good to do on a retreat or other extended activity, but it can really be done in almost any setting. 

Step one... ask each youth to memorize a short scripture that speaks to them about some facet of their life.  (You may have to provide a list of suggested scriptures which you prepared in advance to make the selection process easier.) Next, once they have memorized the scripture, have them recite the scripture from memory to one of the leaders.  If they successfully recite their memorized scripture, the scripture is written on the palm of their left hand like this... Matthew 18:20.  Use a Sharpie or other permanent marker so that this new "tattoo" lasts a while... even if they wash their hands. 

The next part of the challenge is to share your scripture and the reason you chose that scripture with ten friends from the group.  Once they have done that, have them return to one of the leaders who will then draw a cross on the palm of their right hand symbolizing that they evangelized to ten of their friends... in essence, they became the right hand of God within ten people in their circle of friends.  If you are doing this on a retreat, start the process on Friday night and challenge them to complete the evangelism by Saturday night.  Another really powerful thing to do is to use those scriptures as the readings for your worship service on Sunday with each person sharing their scripture from memory and then showing the group their cross "tattoo" symbolizing the faith steps they have taken during the event.  I know young people who are in college who still remember their scripture from years earlier.