One thing you could go around doing is browse the forums and make posts everywhere, and generally increase activity. If you found a helpful/witty/worth noticeable post just like them and someday you'll get a like back. If you found someone who posted around nicely and made many posts deserving a like, then you can friend request him and v.message him. The problem is, unless you do something noticeable, you won't get noticed.
So other than nice users welcoming a person, he/she gets to start at the bottom. So it's good to get some friends along the way (and sometimes meet them at fun events such as the Get Together), but you can't expect anyone to help you around when you're new. Probably that's the reason why new users quit so much. That's why most dedicated PC members (other than the long-time users) have something to do with Creative Discussions (RPs, fanfics, ROM Hacks, GD, GFX & Art etc.) that make them dedicated to this forum while doing something fun and productive themselves. Many a PC member's story is that he/she joined PC at the beginning to ROM Hack/RP/Fanfic/GD/Art.
... right, so I can ramble A LOT sometimes. The thing is, posting around the forums on random topics on Pokémon discussions can become boring very fast, so people who join "just because they love Pokémon" often leave pretty fast. It's often you see many people posting here and there on the forums on ROM Hacking questions, right? Just give it a thought...
Regarding the buddy system, this above may explain another reason why new members are not very interested and leave so fast.
The forum gets really big clamping all these topics, but like I said, it's nice to confine yourself to a certain "home" forum (preferably one in Creative Discussions) and slowly extend out. Another thing a new user can do is welcome other new users saying he/she is new too and find a new friend who is a new user. I reckon this helps make friend fast, but doesn't really improve the "PC is too big" thing.