Companies will use various measures to try and track down debtors such as skip trace reports and background checks. If they are able to find you, which in the world today is usually pretty easy given all of the technology that we all use, they will serve you at your current residence.
Your ability to pay the debt will not prevent the companies from getting a judgment against you. However, they are usually willing to try to work out some type of payment plan on a lesser amount prior to going forward with getting a judgment.
They may, or may not sue. You may simply wait until they do, but in the meantime, you should consult with a debt defense attorney who can review your situation, and analysis options, which may include settlement of the debt, defending against any lawsuit (if and when it happens), defending against collections, and/or bankruptcy.
If you are asking whether it's possible for a process server to find you if a lawsuit is filed then the answer is yes. As to whether someone can collect from you that depends on various factors. It's advisable for you to sit down with an attorney to discuss your specific facts and determine your legal options.