When you say contest, can I assume there is a prize of sorts at the end of it?
If so, how do you know if it is a prize that motivates your team to get involved in the first place? Have you asked them?
I would write a team-mail out asking your team what THEY would like as a prize. If they tell you its TCredits or gift cards etc then you know that there should be sufficient interest from them to be involved in the contest!