^ that one is great because it lists trails by level of difficulty, so it's easy to pick out the beginner hikes. As for groups, there's a huge list here:
Outdoor Clubs in Vancouver - Hiking, Cycling, Running & More
If you can't find a group, a lot of the beginner/intermediate hikes on
http://www.vancouvertrails.com/ are well-travelled and if you're friendly enough you can sometimes find a group of other friendly people who are already there, or at least feel safe knowing you're surrounded by people of varying levels. In Whistler, Garibaldi is a good one. It's nicknamed "the cattle trail" because it gets pretty busy. The views are stunning, though, so it's well worth it. It's also pretty beginner friendly, even though it's listed as intermediate.