1
general::
Phrase(s): Search me.
Inf. I do not know.; You can search my clothing and my person, but you won’t find the answer to your question anywhere near me. (The two words have equal stress.) • Jane: What time does Mary’s flight get in? Sally: Search me. • John: What kind of paint should I use on this fence? Bill: Search me.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
I don't know the answer to that, as in Where's John?? Search me, I haven't seen him for weeks. This expression in effect means "you can investigate me completely for the information you want but you won't find it." [Slang; c. 1900]
American Heritage Idioms