The most successful ICOs in the past did not rely on Google Youtube or Twitter advertising. Ever heard of influencer marketing? They take on people with huge networks, make them either ambassadors of their projects or get them to write about the project or make videos about it. That sort of advertising is not banned, as it is not unsolicited. These guys have a lot of followers and they tend to trust them about the projects they talk about. Much more effective than direct advertising that no one clicks on in fact.
If Google and facebook bans the ICO, does it affect our participation in the bounty?
Not at all. They are banning advertisements, not posts. As far as I know only Medium (the blogging site) is the one that is also suspending user accounts for participating in bounty related topics. You can still use facebook pages to post about content, and you can even still make posts, this is still allowed. The advertising referred to that is banned is the paid ones (where you see them as clickable ads). Unless I am wrong of course, but I am pretty sure of this.