I recently launched a matchmaking/dating app and am wondering how many users we need to gain before VCs would be interested in investing in a Series A. We've done some PR and marketing and are trying to plan out additional marketing efforts with the resources we have available.
There is no definitive answer to this question, since every VC has its own criteria. Also, the total number of users is just one metric - there are others that may be more important to a given VC or in general, including the rate of growth, the engagement, the revenues, etc. But, in the most general sense, if you get to 10 million users within a couple of years, then that starts to look interesting. Unfortunately, the last I heard, dating apps have really fallen out of favor with investors, in part because it's very hard to come up with a viable business model, so you may need even more impressive traction to overcome their fears.
The number of users is not the number for VCs. They are looking for the new 'unicorn' before it becomes a unicorn, i.e. they are looking for an exponential growth or, at least, a possibility of such.
In today's market condition, VCs are very tight fisted in making investments. So I hope you have figured out a viable business model to make this app profitable before you invest any more time on this.
It's not the actual number of users, but the traction that matters at this stage. Take a look at https://venturefund.io that helps you pitch on the basis of your growth metrics.
I question the premise that a single metric (as the question is framed) will cause investment. Of course if your run rate after a few months from launch is 10,000 BALANCED uers then sure, that's a good number; but it probably doesnt apply to your situation. If you had 1,000 users, but with some combination of compelling IP, team, model, then you might get more interest than what user acquisition stats alone can provide.