Following Up for Job Submission

Wanted to see how frequent others send follow up emails as far as job submissions go and how often after an interview
I have applied to many ID job postings online in the past, where I never get a response back on my submission, only to then get an email weeks later that I did not get the job. Others have said that you have to be persistant with following up to really let them know your interested. Many times I see job postings with an online app only and no contact email, how would you follow up in this case?