If you are looking to promote cryptocurrency, both Google and Facebook are not crypto-friendly platforms, so try Twitter, Reddit and YouTube.

Twitter: The platform manager is interested in Bitcoin, you can pay for some popular accounts and get a good promotion.

Reddit: You can buy some ads but stay away from the bots.

YouTube: It is the best place to promote but you need a channel with more targeted content and then you can view the contents of your currencies with them.

Try to use this forum and you may find the cheapest way to promote.