bottom right of the screen, looks like a magnifying glass

I see that thanks.. but for a specific individual or interest similar to Twitter?

click that search icon, click humans, type in keyword .. ie .. i just did fitness ...

search for their name, user name or keyword in everyone's plurks?

You are smarter then/than me

Okay, now we are getting somewhere!

not smarter, just luckier to figure it out first

alternatively you can try Plurkerati