@ksietsma There was once a Mastodon <-> Twitter bridge to help make those connections. But that has been off for a long time. I think Twitter API did not like this tool.
I’ve gathered a few tips on how to transition from Twitter to Mastodon a while back. Haven’t updated it since. But some might still be useful:
@ksietsma AFAIK you'd have to search on every instance you think they might be on
@ksietsma That is a tough question to answer. Because if our instance has never seen that person account from our instance, our search results will show nothing. Best is to ask people directly for the Mastodon account. I saw once someone put up a search engine for Mastodon account. But I can’t remember the link. Not sure if it is exhaustive. And people might have multiple accounts.
I suggest putting your Mastodon handle directly in your Twitter profile. It will help your followers.