From what I have noticed, two different groups exist in any teen ministry. One, usually the younger group, wants to play, have fun, and just plain "hang out." The second group often wants similar things, but also desires a deeper relationship with God, and want more spiritual food than group one. The trick is to balance fun and learning. If you group is mostly type one, then just have fun. Always incorporate lessons and praying, but focus a lot on fun. Type two needs deeper Bible study, debates (maybe), and prayer. Arrange prayer groups of at least 3 to a team. (They will not only pray with each other, but correct each other and whatnot. Don't do group with two people, sometimes it can become abusive.) The ultimate goal is to get all type 1s to be type 2s without them realizing it
(Still however realize that even type 2s need fun!)
As for numbers, get more. Take inventory of what you have now, and really strengthen them up. This early on, don't shove doctrine in their faces, but build them up. Get them feeling very confident, but also prepare them. Send them off in twos or threes in the mall (or wherever they hang out nowadays) to meet new teens. Also, have them try to bring their friends fom school to the events. Realize that most non Christian friends are type 1s thinking everyone else is going to be a type 2, if that makes sense. They want fun, but expect events to be boring. So make events where a lot of guests are involved more tailored to type 1s: Pray at the beginning and end, but focus on fun.
Well, I hope my rambling helped you in some way
God bless