The 'Thriller' song has become really popular after his death, because of his fans who, every now and then, gather (in various places around the world) and pay tribute to him by dancing the 'zombie' part of the song.
Also, 'Thriller' regains chart success because it is a Halloween-related song, and almost every year (after his death) the song is always placed high on Billboard's Streaming Songs chart.
The 'Billie Jean' song regained chart success, when it entered the Top 20 of Billboard's Hot 100 in 2014 (this was mostly due to a YouTube viral, live video by a fan who recreated the singer's Motown 25 Performance of that song).
Although not a song from his adult solo albums, after his death 'We've Had Enough' has become popular, especially among his die-hard fans, mostly because of its timeless, social theme.