I had no search bar for some time too. I searched by creating a post, because it suggest you similiar threads. It suddenly appeared, cant recall when and why :/
I just read in another thread for new members:
"Why can't I access private messages, chat or the search bar?
To do that, you need a certain amount of contributions - we can't tell you the exact number. It doesn't matter if those contributions are comments or threads, both count towards the threshold amount. Do not spam low-effort posts though unless that fits in with the nature of the respective thread (e.g. posts asking members to post in one word what they are feeling)."