This page is up to date in April 2020, it is suggested to the Applicant to exert caution and trust in priority the New Member website.
An applicant to the "Debian Developer, uploading" or the "Debian Developer, non-uploading" must get at least one advocate who must already be a Debian Developer. Although it's not stated explicitly, one hoping to get the upload rights should probably get advocacies from Developers having the upload rights or a well known experience with packaging.
Advocates can normally submit advocacies through visiting https://nm.debian.org/process/XXX/advocate and post a signed message.
The message can be wrote in a plain text file, using one's favourite editor, and then signed using a command like cat text_file|gpg --clearsign --default-key $ADVOCATE_KEY_ID.
Normally, the command to use is suggested on the Applicant's advocacy page.
After submitting this signed statement (the message along with the GPG signature obtained through the recommended command) through the form on the appropriate page, this step is done.
I can't get a Developer to advocate me, or my sponsor has gone MIA
If no Developer agrees to advocate an Application, then the Applicant is probably not ready yet to become a Member of the project.
If the people the Applicant was working with went MIA, the Applicant should probably try to get in touch with people having worked with these MIA Developers or in common fields, to see if they would accept to review his work and advocate them.