The Collaborative International Dictionary of English v.0.48:

Inquirer \In*quir"er\, n. [Written also enquirer.]
   One who inquires or examines; questioner; investigator.
   --Locke.
   [1913 Webster]

         Expert inquirers after truth.            --Cowper.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inquirer
    n 1: someone who asks a question [syn: inquirer, enquirer,
         questioner, querier, asker]