Hey Katrin Dombrowski,

first of all I'd like to apologize that it took so long until you got an answer here.

I'm closing this feature suggestion, because it's very much possible to search inside of microblogs. For one, there's a search icon at the head of the microblog itself. Also, if you use the standard confluence search microblogs will also turn up within the search results. You even can filter down those search results to show only microblog posts and nothing else. :)