Hi there. I have some answers.
I was "on hold" last year when I applied- it was bad last year. This year when it happened again, I was determined to get off the list. My UCSD hold turned into an interview. Let me tell you
how.
You need to send a letter of APPEAL FOR INTERVIEW in your subject title, address an email to the adcoms and send them an update on what you've been doing since your application. Is anything new? Did you learn anything in your place of volunteering that you think would strengthen your application? Are you fluent in a language and are you using it daily (this was a big one for me- I use Spanish about 85% of my day with patients). Any new skills? Go into depth on an activity that you couldn't really talk about. Be real. But DONT simply say "I want to go here" stated over and over.
If you don't believe me:
1) Call the admissions office and ASK NICELY if they have a moment to answer a question for you. The staff are just as important in this process - they can make or break your application. I'm convinced that a woman at one of the UCs got me off the hold list. I had sent her a thank you note, and she also thanked me for being exceptionally polite. They must get some demanding applicants (understandibly frustrated).
2) Say "Hi, thank you so much. I'm on hold to interview and I'd really like the opportunity to demonstrate to the committee that I'd be an excellent matriculant. How can I move my status from "on hold" to being invited for interview?"
3) Do what she says.
Best of luck! UCI hasn't contacted me yet, but it worked at SD.