Mashallah good Ramdhan Itikaaf/Retreat taking place at Upton Lane Masjid. I only could spare time to go for a brief moment but seemed engaging/interactive i.e not your mundane type of event.
As long as they are not going against Islam, why not? Actually it might be recommended, specially: using language that is common with the youth, using sports e.t.c. to bring them in, being light hearted ( many examples of this from the Salaf) and bring their hearts close to the deen.
Also, how was the youth 'lost'? it was the parents responsibility, and in general the Muslim society's responsibility, which includes the Scholars. If the scholars are not the leaders who give us vision and practical steps to solve our problems, then who will? Also, I think this is not a specific problem to the lands "kufr" and "Batil".
Isn't the general/base ruling of everything (except Ibadat; where the scholars of Usul differ) Mubah? (A scholar can confirm this: I learned that a Mubah with the right intention the raise it to Mustahab, so a lot of the youth activities could actually be Mustahab (recommended)?)