This post has some great advice; grassroots-style marketing does take longer but can be built-up over time.
Just make sure to follow the rules of whatever forum you post in so that you aren't 'spamming' adverts.
For example, on my Discord server I keep a dedicated channel for self-promotion, referral links, friend codes, and other such bits. Anyone who just joins up and asks to partner (without having even participated) or tries to spam a link ends up getting booted.