IM TRYING TO LOCATE MY GREAT UNCLE ACTOR GREGORY SIERRA - Stared in Barney Miller, Sandford & Son & Deep Cove

I am trying to Locate Actor Gregory Sierra - He is my grandfather's brother.  My great Uncle - had communication with my mom, his niece Vicki when I was younger but lost communication since then.  Can anyone tell me how I can reach out to him.  He played in Barney Miller, Sandford & Son, Deep Cover and recently in 2018 in a movie "The other side of the Wind"

How would I go about doing that?