Welcome to FH! You're always welcome to approach me c:
Using the forums, joining roleplay groups, or even simply jumping into conversations in the Grounds are all great ways to make friends! As for mate centers and adoption centers, those are advertised by someone and people come in looking to find a significant other for their roleplay character and to find parents/young for your rp character (respectively). Nowadays these seem to be pretty rare, unfortunately
I'm sure you'll make some wonderful new friends in no time!!