David Armitage and Sam Rowe join the pair on the outs list, as the Saints have made their first list lodgement of the off-season.
Longer played 57 games for the Saints after joining the club at the end of the 2013 season, while Pierce has five AFL games to his name.
Rowe played his 100th AFL game and only game for the Saints last weekend, while Armitage played 169 games over 13 seasons.
“Billy and Lewis were both unfortunately sidelined for most of the year with injury, but we thank them for their commitment to St Kilda over their time at the club,” Saints General Manager of Football Simon Lethlean told the club’s website.
“While Sam was only here for one season, he has had a great impact on our group.
“As the club communicated last week, we also thank David Armitage for his incredible service over thirteen years.
“All four men have made important contributions to St Kilda, and we wish them all the best for the future.”