YouTube is mind blowing profitable. Just look into Alphabet's corporate earnings.
The average video ad costs the advertiser about $.30/engagement. So if you watch for more than :15 or click the ad, the advertiser pays YouTube $.30 and YouTube then gives a cut to that channel's owner.
As for Twitter they are finally turning a small profit. They finished 2017 with net income of $38.7M.
1Q 2018 was even better.
"This quarter shows the monetization and ad growth machine at Twitter is finally heading in the right direction after years of a 'one step forward two steps back' strategy," wrote GBH Insights analyst Daniel Ives in a research note to clients.
In our experience however, Twitter ads are by far one of the WORST preforming ad options available for webcomic promotion.