Stonestreet, 41, had split from his long-term girlfriend Katherine Tokarz and he is said to have fallen head-over-heels for his good friend Theron, reported Contactmusic.
"Charlize and Eric get along incredibly well. They started off as friends but things are blossoming between them. Eric is down to earth and funny and Charlize thinks the world of him. It's early days but they're very fond of each other," a source said.
The 37-year-old "Snow White and the Huntsman" star, who adopted a baby boy called Jackson last May, has been single since breaking off her nine year engagement to Irish actor Stuart Townsend in 2010.