Realtors could use internet for being a Marketing Arm of their current efforts.
Email: They can send emails, visual presentations via emails.
They can put out visual presentations on their websites and get on Search engines.
They can put out Classifieds of their listings.
They can write blogs that strikes buyer's interest and be the most trustable realtor.
They can use Search engines to locate homes, neighborhood etc. outside their locality and help potential buyers make better comparisons and decisions.
If I have left anything out here, please let me know. Banking on 'people connections', it maybe hard to develop new clients, maintain current and previous clients.