While the use of a brand or mark would not so much be a copyright violation, you could very well violate trademark rights in doing so, particularly if the purpose has any commercial context. You should consult an attorney with more specifics.
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Since you don't know the difference between copyright and trademark, you need to get to know an Intellectual Property lawyer who does, and ALL IP lawyers will know the basic difference. Since YouTube is not promoting your FB, Tw, blog or site, it is illegal on several counts (including 15 USC 1114 and 15 USC 1125) to falsely imply otherwise by using YouTubePromote. "YouTuberRetweets" is likely also illegal but closer to the legal borderline, since YouTuber implies a user of YouTube rather than YouTube itself. "YouTubers Unite" is likely legal, both on free speech and descriptive use grounds. However, I feel confident you are engaging in copyright infringement due to the content you are using and the way you are likely using it. To reduce your risk you need to consult an IP attorney for some needed guidance. If you don't consult now you might very well be consulting later at much, much greater expense and risk.
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How you use the name will determine if it is a Trademark (not copyright) violation. This is a tricky area, and you should consult with an attorney who regularly works in the area of Trademark and Internet law.
You may want to discuss your situation with a lawyer in more detail. Most lawyers on Avvo, including myself, offer a free phone consultation.
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It would arguably be trademark infringement and/or false and deceptive advertising as you are creating the impression that you are somehow associated with or acting with the consent of YouTube etc. unless your use falls within a very narrow "fair use" carve out. And even there it's tricky. By adopting a third party's brand identity/trademarks you are likely creating confusion, and/or the appearance of endorsement or false association. That's legal talk for creating a world of hurt for yourself.
Hire a trademark/brand rights lawyer and get some good advice on the front end before sinking money into your brand development, etc.
This is not legal advise. Just my thoughts.