I hate phrases like that.
Did the youth encounter Jesus? Then I would call that success.
Hopefully some came to know God. Hopefully some went deeper in that relationship. Hopefully lives are transformed.
In John 4/37-38 Jesus briefly discusses one harvesting and another reaping. In I Cor 3/5-8 Paul discusses one sowing, one watering, and another reaping. In this light, westernized concepts of "success" melt away.
For years I wasn't sure how much impact I was making as a youth minister. It turns out the real fruits are not always evident until later. I found that I had a lot more than I had known. Yet some of what we all deemed successes then don't look like it now. I continue to trust, pray, and love and hope they will be. Not for my sake, but for theirs.
And there is, I think, another component. Did it transform you? Did you grow in love and grace? Did you grow closer to God, the youth, and their families? Basically, did the great commandments become more real? Do you see more fruit? There's some real success, too!
If we define success as the world does (regardless of how many preachers or local churches go along) we have missed the point, just as anyone who looked down on the widow for giving such a pittance (Lk 21/1-4) had missed the point. Clearly Jesus judged otherwise.
We should be the Church in the West but we are too often the westernized Church.