You need followers in order for your promotion tweets to matter, right? If you've already got plenty of those, wouldn't you also have plenty of subscribers on youtube, which kind of negates the need to use twitter to promote?
Yes, you need a following. No, this doesn't mean you already have a YT following.
The thing is, you need to use the platform as is intended. Twitter is a place for short life updates, opinions, jokes, etc. It is text based, if you're more inclined to share photos you might want to turn to Instagram. A lot of people already have had a Twitter for years and have a few 100 or maybe even a few 1000 followers, which just accumulated throughout the years. This doesn't mean that this is automatically connected to your Youtube account.
If you do not have a Twitter yet and are going to start one for your YT brand, DO NOT only advertise on it! People will see that all you do is plainly advertising your channel and won't follow you. Post entertaining and/or interesting content on your Twitter, work with a lot of hashtags (especially the trending ones) and build a following from there. Once you have a bit of a following, you can start directing them to your page, if the video is relevant to the content your posting on Twitter.
For example, if you do videos on politics and you post a political opinion on Twitter, you could link to your video in which you talk about that particular subject. Avoid just posting 'New vid up, check it out!' with a link. Because that is not going to work until you have an established YT following that started following your Twitter THROUGH your Youtube (aka, they're already subscribers).
Hope this helps a bit!
