Bonjour Irving,
As a general rule, you will pronounce the -s when "plus" means "more" and the -s will be silent when "plus" means "no more/less" as part of a negation:
J'ai plus d'argent que toi = I have more money than you -> [plus]
C'est le plus intéressant = It's the most interesting -> [pluz]
Je n'ai plus d'amis = I don't have any more friends => [plu]
Take a look at one of our partners' link about the pronunciation of "plus": Plus pronunciation
I hope this is helpful.
Bonne journée !
