This is the problem with discussing these sorts of issues. If my experience isn't what you've seen, I'm making assumptions about something I know nothing about (actually, I'm just talking about what I've seen IRL, not what I've read online or seen on TV). If a church or pastor is doing something contrary to your experience, they're doing it wrong. When the stats reflect increased risks for kids who take purity vows, it is because the parents are doing something wrong. In other words, you "own" the successes and the good intentions but disavow all of the drawbacks.
I form my opinions based on my own experiences. Around here, girls wear purity rings, not boys, not even when they're from the same family or congregation. Some are just jewelry while some have the message engraved on the outside of the band. Around here, church youth groups do involve recruiting in a low-pressure sense - kids are encouraged to bring friends, a couple of the bigger churches out in the country have a bus that picks kids up in town to go to the group, they serve pizza and host dances and other teen-friendly events that are open to the public and advertised via flyers around the community. And there is very little parental involvement in these youth groups; unless the parents belong to the church hosting the group they most likely wouldn't know the specific content/topic/activity of any given meeting until after the fact.