1) Admirer 2) Booster 3) Champion 4) Friend 5) Motion endorser 6) Motion mover 7) One who say Amen 8) Protagonist 9) Supporter 
• (n.) One who seconds or supports what another attempts, affirms, moves, or proposes; as, the seconder of an enterprise or of a motion.
Sec'ond·er noun One who seconds or supports what another attempts, affirms, moves, or proposes; as, the seconder of an enterprise or of a motion. 
[n] - someone who endorses a motion or petition as a necessary preliminary to a discussion or vote
noun someone who endorses a motion or petition as a necessary preliminary to a discussion or vote