How to finish Master's Thesis when my adviser is too busy to help me thoroughly edit what I have written? I have finished my B.S. and I am now finishing my M.S. thesis (already finished M.S. classes). My original thesis topic was not getting me anywhere and I came to my adviser asking him to allow me to switch to a new topic that I have already started working on. The professor allowed such a change and I believe my new work is much better and more interesting. Unfortunately, the new thesis topic is not my adviser's area of expertise. 

Moreover, I have been late in turning in my thesis for several semesters since I've also been working full time much of the time after I finished my B.S.. This makes it feel like my university does not really care about my success anymore and I am not even being pressured to finish writing my thesis as I would have been if I was a full-time student. 

I will be finishing writing my thesis on this new topic, but much of the work I have done have not been checked by anyone with a Ph.D. This worries me. Should I just crowd-source some comments for editing my thesis from friends and try to just get it turned in and accepted so I can present? Or should I seek out more professors who are more familiar with this new topic and try to have them read it (it would take at least several hours to do this and, keep in mind, I am not a full-time or even part-time student right now)? 

I think my work is good and I will pursue trying to get it published in a journal once my actual M.S. is done, so I am not too uncomfortable with the things I've written.
It sounds like you have two major concerns about getting quality feedback from your advisor: (1) he's busy, and (2) he's not as familiar with your new topic. I'll address these separately.

Getting high-quality feedback from someone very busy

To get the best feedback possible from your advisor, make sure that whatever you send him to review is as polished as possible. If he's pointing out typos and areas where the writing has issues, he's not going to have as much time to evaluate the content, which is where his feedback is most valuable. 

It will also help if you identify and tell him about the areas where you think you most need extra high-quality feedback: "Could you tell me what you think of the formulation in Section 3, I'm not so sure about that part."

Getting high-quality feedback from someone not an expert in the topic

Even though your advisor is not an expert in your new topic, he's an expert in something and he knows what good work looks like. He knows when an argument seems weak and "hand-wavy" and when the evidence on offer doesn't support the claim.  So he's still likely to have good advice even if he isn't as familiar with your topic as you would like.

In fact, for PhD students at least, it is generally assumed that the student knows more than the advisor about the thesis topic by the time the student is about midway through the program.

On crowdsourcing thesis feedback

Having said all that, it's still useful to get comments from others in addition to your advisor. 

Ask your friends to read your thesis to (1) find typos and obvious mistakes, and (2) note areas where they think something is unclear, so you can improve the writing. This will help you make sure the version you send your advisor to review is as polished as possible, so you'll get better feedback from him. 

If you know some professors who are expert in your topic, you can send them a copy, but follow the advice for getting feedback from someone very busy: Make sure what you send them is very polished, and identify where you want their help the most. If you don't know any professors who are expert in your topic, then after your advisor gives you his feedback, ask him: "Do you think we should also send this to an expert in the topic for review? If so, do you know anybody we could send it to?"