The fire broke out just after 7:30 a.m. Monday near Belmont and Mariposa.
When crews arrived they saw homeless people walking out of the building and were told that one person was still inside. However, after gaining control of the fire and conducting a search, crews were unable to find anyone.
Fire officials say the building was a vacant boarded-up business with the wording 'Sew & Vaccum' on the outside of it.
This story will be updated as more information becomes available.