What do we do about a missing sibling and a piece of inherited property

My 4 siblings and I inherited a parcel of undeveloped land in south Florida. My elder brother, the executor of Daddy's estate, has recently passed. My sisters and I would like to sell the land, but our other seems to have gone off the grid. No one has heard from or about him in 3 years. His name is on the deed as well. We have contacted police, his former residence, and other records such as death and hospital. SS says his number is still active, but legally they can't tell us anything more. We can't afford a private investigator. Where do we go from here. Is there anything we can do to circumvent his signature if we cannot locate him?