We are a team of designers and developers with expertise and experience in Web designing, HTML, CSS, PHP, AJAX, JQuery, XML, Wordpress, Bootstrap, CodeIgniter and MySql. We have developed this feature "refer a friend" for a few sites.
I have read your requirements and will be able too deliver as required. I would like to see the site where this needs to be implemented. Users are being saved in database? We need to add a scores field and keep increasing it each time a "referred friend" signs up.
I ensure a very thorough job and also support if you need changes / enhancements in future. I look forward to hearing from you and working on the project.
You have a few projects to your credit and I will consider it a privilege to offer my services to you. I look forward to this project as an opportunity to establish a long term association.