... I see no reason why you couldn't use a facial moisturizer on your neck.
I agree with this statement, after buying and trying many "neck" products myself.
I started a thread about "Facial Yoga" elsewhere on this site, and so will just mention here that there are exercises that target the neck and throat. I've been doing them for probably six months, prompted by a major weight loss and fears of sagging as a result.
Anyway, I did a search and found a site that had alot of great exercises. Go to www dot dermaxime dot com, and click on "FREE Articles" in the column on the left side of the page. A whole bunch of interesting articles come up, including "Facial exercises", which will include exercises for the face and neck.
[Disclaimer - I am not promoting their products, nor do I know anything about this company, nor do I care. I just "googled" neck exercises, theirs came up, among others, and I found their site useful].
Give it a try! I have been pleasantly surprised by the results.