Ask HN: How to get initial traction for crowdsource review platform like Yelp?

Hi awesome people at HN village,

I am working on a crowdsource review platform for technology tools, but is encountering some roadblock on getting early user.

The problem is, in order to make a crowdsource review platform useful (besides a complete database of tools), there need to be a lot of user reviews to begin with. However, without initial user to post review, the platform is not that useful. So it becomes a chicken and egg problem. I am wondering how Yelp and other similar service did it at the beginning stage?