This is the problem I see with all the companies who firstly believe in building products rather than;
Got positive response, create an interest capturing page offering time-sensitive free access or discounted early access once the platform goes live.
Rest you can try adding your product to SaaS communities & directories in a sequence of getting immediate boost i.e. IndieHackers, ProductHunt, Betalist, SaaStraQ, Facebook Groups, Subreddits, GrowthHackers, Capterra, G2, TrustRadius, etc.
#copied from my Quora reply
how do/did you analyze what's going on in the group, and how do you catch the member's interest?
This is really good advice, thank you for sharing.