Auto promotion (groups in VK, in other social networks) how is it for you?

Question

Search Engine Optimization

I know that there is a botanist, but it was so long ago and it seems to me that he is already in the past ..
How else can you find people?
There are services (paid / free) like Cerebro, so that he would not just add anyone, but "interested".
For the money, there is, but not much.
Who has used this promotion, how do you like it?
Or can this money be spent on advertising?