How did you know it was a plural?
If it were singular, it would be "ich mag den Teller". It's the same in English. You don't say "i like plate", you say either "I like the plate" (ie use the definite article) or "I like plates"
I wrote "Ich mag Tellers" and it said I used the singular, not the plural. Is it correct? Plural without the 's' and singular with the 's'?
This word doesn't change, only the definite article : Der Teller - Die Teller
Why it can't be DIE Teller?
You can't say "Teller mag ich"?