This amuses me. You are looking for a co-leader.
1. Why not recruit a co-leader from the members you already have?
2. What do you need a co-leader for? Is the leader overworked?
3. If the leader is overworked because the members aren't good enough to become co-leaders, is getting a co-leader the top priority?
4. If 3 is true, shouldn't you be looking for new members?
5. If 3 is not true, I still want to know why you need a co-leader.
6. And what do you want the co-leader to do? Extension of the above.