Yeah Instagram or Tiktok are the major ones, and you'll definitely see that some popular accounts on Reddit have Onlyfans as well.
Reddit:
When it comes to Reddit, find a subreddit you're interested in, and click on "Top", then set it to "All Time". Those users will almost always have an OF, simply because they see the benefit as they already receive thousands of likes.
Instagram:
On Instagram, once you follow a girl, you will instantly be shown other profiles that are "Suggested" as they are similar to the one you just followed. I should warn you, you can fall in a rabbit hole and be there for hours following random thots and trying to backtrack to collect the ones you missed. The + icon in a profile does the same thing as "Suggested".
Like the others have said, a shocking number of Instagram models, including but not limited to Twerkers, Yoginis, Contortionists, Gym Babes, Fitness Trainers, and more will have Onlyfans. Look for a link in their description, which will usually house different tabs, which one will say "Exclusive!" or simply "OF".
Usually, when you've followed enough, you'll notice a lot of them are personal friends with eachother, echoing what
GreaseMonke said:
You'll notice a lot of the girls you've followed from the Suggested are friends with the others, and some will do collabs. This can be an addicting process, but is an easy way to discover OF girls on Insta, and I've been collecting them for a while.
The + icon in a profile does the same thing as Suggested, so you don't have to unfollow and refollow to search for more.
For an easy way to come back to a profile you're not sure about later without following right away, bookmark a post on their page and file it under where it belongs (Yoga, Fitness Girl, etc) and/or, if you want to be messier, DM a post to yourself.