How can I encourage users to sign up for my new social discovery website?

If you have a good amount of traffic, I would like to know first how is that traffic finding your link on social media? Are you actively pushing your content through to them or are random people coming to your profiles and or posts? Are you boosting ads?
If you are boosting ads - your problem could be wrong target audiences and or wrong messaging plus wrong landing page ---> which leads you to having the wrong type of offer to the conversion.

If you are pushing the feed to random users yourself, you could be using the right words for them to be curious on social media but then they may realize that it wasn't what they thought it was.

Also, whether you have an app or not, is important to always think of SEO as a growth / user acquisition strategy effort which means that you or an agency (like Unthink) has to do its homework and create the right target for your content so that is organically found by them.

Once you having traffic coming in you can always A/B test everything so that you can see what's working and what is not.

If you are interested in further reading, check out this article:
Best SEO Practices To Increase User Base Naturally Through Google.
http://blog.unthink.me/seo-best-practices-to-growth-hack-startup-user-base

--- Unthink Digital Marketing is a full service subscription based marketing agency offering everything from simple websites to full developed apps and content marketing strategies through Hubspot. Visit www.Unthink.Me for more information.

You have to analyze the bounce analytics. This is like an X-ray and Ultrasound test of the body. Then we can find out why users are not signing up and how much time they are spending on the pages and which pages they are browsing?

I can do it for you.

On the plus side, you are getting some good traffic. The question is what type of traffic. Try to find out if bots are making up any percentage.

Also ensure your correctly identifying where you target market resides. People talk about penetration rates with broad campaigns with no focus. If you are operating within a specific niche whether it is language, geography, subject matter, then focus your marketing communications to services actively engaged by those niches. You may find a higher number of sign-ups with a much lower amount of traffic.

When it comes to messaging, survey existing users to determine what brought them to your site and why they signed up. This is a biased view but it is a starting point to understand key traits of successful conversions.

Perhaps you need a serious heuristic evaluation of your website i.e. a UX expert review. UX means User Experience and as a UX professional with over 4 years industry experience advocating for users of digital products, I'm able to quickly map out your users' pain points (frustrations) and how those can be turned around to maximize conversion for you. You should give me a try. Look up my portfolio on the web - uxyemi.co.uk