* The name is misspelled. Double-check the spelling to see if you've got the right person.
* The person is not well-known. They might be a relatively unknown actor with few credits.
* The person is not an actor. They may be involved in the film industry in another role, like a director or producer.
If you can provide more information about Jason Warren, such as a possible year of birth, or any other details about their work, it might be easier to find them.