How to predict the growth of the community for the customer?

Question

Marketing

There is a company, let's say Aeroflot, and there are a number of social networks, for example, VK, FB, IG, and there are also subscribers, but previously the communities were extremely unprofessional and therefore there is no clear growth data because they jump at the bottom, so the customer wants to know how many subscribers we will have by the end of the year and how many will be next year.
How can one make predictions in this case? What data to rely on? What formulas to use?

Answer 1

Well, run an ad, see the increase, approximate

Answer 2

Subsribers = 53*5*K*M + 53*2*L*N

Answer 3

At school and university, in laboratories, they taught how to build a graph by experiment - use this knowledge to build and fit a curve from your current data
After plotting, compare it with graphs of various functions
Estimate how feasible they are
Also, do not chase the number of subscribers - it is better to increase conversion