Does effort have a plural form?

No, the noun effort is an generally an uncountable noun that has no plural, a Word for the force or energy required.

• You need to put more effort into completing the assignments on time.
• A lot of effort was required to save up the down payment.
• With time and effort we produced a crop of vegetables from our garden.

The only use for a plural is as a Word for serious attempts or the activities of people who are working together to achieve a particular goal; for example:

• Her efforts were rewarded with a new contract.
• Our success is due to the combined efforts of many people.