A multi-user search system with methodology for personalized search query autocomplete. In one embodiment, for example, a computer-implemented method includes: receiving a search query having an incomplete token; generating an index key that is composed of both (a) an identifier of a document namespace that a user account associated with the search query is authorized to access, and (b) the incomplete token; accessing an index dictionary with the index key to identify a plurality of index tokens, each index token of the plurality of index tokens having the identifier of the document namespace as part of the index token and having the incomplete token as a token portion of the index token or as a prefix of the token portion of the index token; iterating over the plurality of index tokens until a stop condition is reached; and returning an answer to the search query based on the iterating.