You need a “Front End Designer” OR you need someone “who can develop a cool theme for my startup”.
Both are not the same and rarely covered by the same person.
Posting your budget and more info than just “theme like xxxxxx.com” would definitely bring more leads and contacts from serious developers and designers and not just the usual “I-can-do-everything-kind-sir-contact-me-for-details-dear-sir” Joe’s and Jane’s.
Purely for your information - a decent working and relatively good looking app with the functionality that matches your example would cost several thousand $ minimum from any developer worth working with. (Let alone the backend setup and configuration you would need to run it).
You know that app raised several million $ to get where it is now right?!
I would be highly suspicious of the eventual quality from anyone who says they can do it for much cheaper.