Befriend another popular character (or another character period).
I know it sounds weird, but trust me. Most players are more than welcome to roleplay with someone new, however, the task of taking the first step is up to you.
As with most things, you cannot expect something to come to you without doing anything yourself. Put your character out there, try to join conversations, meet new characters, etc. Yes, many of those attempts will probably not work out and you'll be told to 'screw off' but guess what... even that is some sort of roleplay which is better than nothing.
All it takes though is a few good attempts. After a few chats where they respond positively, you exchange numbers and become mates. Then you can become mates with their mates, and all of a sudden you're not just a background support character but a main character of your own.