If you fall out of touch with your internet leads send them a simple email, don’t over think things. The below email works because your offering help and asking for a simple short answer.
Remember the leads from 3-6 months ago are the ones that are getting ready to buy soon.
Subject: House Hunting
Hey I just wanted to check how your home search is going? is there anything I could be doing for you while you browse online?
Sent from my iPhone