User Record Field type in records

Hi All,

In the database the createdBy field holds "userid@test.com" which is the userid of the user. When i create a recordist using the respective table and have the OOTB search on createdBy field to get the record on  using  "John" or "Smith"  as the search value , it doesnt return any record. But if search on email return the data. ( Note: John and Smith is the first and last name of the user). The custom grid in front end holds the Display field using user function. But as the recordlist is created on userid , search on First or Last name is not returning any record.

Multiple options tried: 1) Created a custom field , but user function cannot be called in custom field 

                                   2) Changed the data type field from text to User type  in the mapped fields of RecordType and called in recordlist . Still not success  , how the datatype conversion from Text to User is used.       Maybe i am doing wrong here?

How can we leverage the OOTB search here instead of create a whole new search text box and its logic convert the first name and/last name to userid and then search.

Thanks in advance, appreciate the response.

Raj