Devon
I'm so sorry to hear that. When something like that happens it is a real struggle to understand what God is doing in it all. I agree with Edd, I think we're living in a broken world and thus not immune to rubbish stuff, but there is a mystery of faith whereby God is alongside us in it, and because Jesus experienced brokenness in its most raw form he is able to empathise with us in the most profound of ways. So sorry.
Madmomma - gosh, what a sad experience of alpha. All I can say is he was actively going against what the manual advised - I've done it a lot now and it's all about gentle listening and never about imposing dogmatic statements. What a lack of compassion - I'm so sorry. There are other courses and other churches which you might feel more welcomed into. 
Cish - 20s is the most under represented group in most churches. We have a few, mostly parents of young children - I'd love to have more single people in that generation. We're starting a 20s group as it can help to identify with others, though equally some love the home group system with its more multigenerational approach, I guess there's room for both. With the parents we have a very thriving and welcoming toddler group, Bible study etc. It's actually a growing section which is fab. But I don't really know the answers for the age group in general - we have quite a few teens but they all tend to go off to uni then settle elsewhere.
I've been to churches with a huge amount of that age group though - used to go to a vineyard church with hundreds of 20s. Lots of donuts and good coffee, but more to the point really good quality of teaching and good system of small groups so people can feel welcomed in and not too overwhelmed.
Sorry for the essay!!
I'm busy on last minute rewrites and have been quite poorly, so sorry for absence lately.