React.js Developer for Interactive Web Application

I need a proficient React.js developer to build a dynamic web application tailored to a diverse audience - the general public, business professionals, and students/education sector.

Key Functionalities Required are:
- User Authentication and Login: The site should secure and manage app users' identities, sign-up, sign-in, sign-out functionality included.
- Real-Time Data Updates: The website needs to possess real-time functionality so information is instantly updated and displayed to users when changes occur.

The primary purpose is to create a useful, interactive digital experience that can cater to a wide demographic.

Ideal Skills and Experience:
- A proven track record of developing applications using React.js
- Solid expertise with user authentication features
- Familiarity with frameworks enabling real-time functionalities
- A keen understanding of making applications responsive and user-friendly to cater to a broad audience, from the general public to educational and business professionals.