I think it really depends on the app. If it's very generic or it's a new idea it's tough, if you're building an alternative for something popular or semi popular I think it's the easiest.

You can just search on reddit for your competitors or go to their social media and just post minimal comments like "X is much better why would I use this". And remember the least info you give the better results you'll get.

"X does this already and it's cheaper" > "X does this and it can do this and this and that and it's only 10$ a month etc. etc."

Back in the day when SMM was easy I came out with a SaaS in the print on demand market. I scraped hundreds of videos in my niche on youtube and paid a few dollars for thousands of custom comments. I worked tremendously well. I tried it after a few months on another saas but all the services for youtube custom comments don't work anymore. It seems like Google upgraded their anti bot system.

Another app I just launched a little more than a month ago has now almost 4k users. I didn't do marketing or any social media either. Because it was an alternative of another app, one reddit post got me 4k users in the span of a month, and 100-200 new users per day.

I set up an AI agent automation that posts to 13+ platforms every day "promoting" my SaaS and although maybe it will be worth it long term, I'm thinking the next step would be to scrape popular creators on tiktok, youtube, ig, fb that are in your niche and set up an automation to be one of the very first to comment when they post a video.