To get traction on mastodon you have to use hashtags. Here's an example from a recent toot:
Looking for a place to discuss #ClimateAction? Consider checking out the new Lemmy instance dedicated to #Solarpunks organizing for a better world over at: https://slrpnk.net
Those two hastags get about 500 combined posts per week, so there's a good chance both have users following them.