If you'd like your (public) posts to appear in search results on Mastodon, remember that you need to opt-in. Edit Profile → Privacy and Reach → Include public posts in search results. 14K people have opted-in so far!
For those looking for setting, or checking, the option on the Web interface go to Preferences, Public Profile, Privacy and Reach and the option
'Include public posts in search results
Your public posts may appear in search results on Mastodon. People who have interacted with your posts may be able to search them regardless'