More than 3K subscribers in linkedin. 60% of which are investors or investment analysts: https://www.linkedin.com/in/ivansologub/
Mailing list: more than 1.2K subscribers, 50% of whom are startups who have passed the seed stage, 40% are financiers and analysts of European funds. At least 35% of the openings of each letter: https://tinyurl.com/tesg8xn
Slack chat is a new undertaking in which a little less than a hundred startups of the Seed round and above. Several investors are the business of angels: http://bit.ly/StartupSchool2020.
Why don't you spend your time marketing your platform directly, e.g. growth hacking, rather than resorting to cheap ways to get followers.
Usually, promoting products wont generate much hype unless these products are already extremely well known.
You wont find many of those on a forum mostly dedicated to new projects.