The only time it's has an apostrophe is when it is a contraction for it is . It's a cold morning. The thermometer reached its highest reading. The following examples demonstrate pitfalls to avoid when using possessive pronouns. None of the neighbors offered their support.
None is a portion word and is plural here because of neighbors .
Incorrect Not one of the neighbors offered their support. I did it myself. Incorrect My brother and myself did it . Myself does not refer back to another word. I would be correct here because it is the subject.