I don't know about Reddit, but for Wikipedia I just write a guess for the title of the article I'm looking for, and if I'm not redirected to the proper title of the article, then I'm normally sent to a disambiguation page. I've never found myself in need of something like Google for Wikipedia.
That works if you know the article you want, but for something more abstract wiki search is terrible
I just came up with this example on the spot, searching wikipedia for "inventor of paracetamol", the first result on wiki search is "Polymorphism", then "Diphenhydramine", then "List of Suicides", then "Menstruation"
Searching google for "inventor of paracetamol wiki" links to the wikipedia Paracetamol page subsection History
Wikipedia search works well for me. The site search is exhaustive, returning every single page matching the query. For topics in the news recently, all changes are propagated to Wikipedia's search index immediately, while Google takes longer to recognize changes.