Ways to grow classifieds site are:
Hire some advertisers:Content is the key element for the search engine marketing (SEM) , You may go for paid advertising campaigns like- Google AdWords to get more traffic to your classified site but once your budget come to an end, your traffic flow will stop immediately.
Advertise your site/business on other classified sites: You can run your classified site's ads on other top classified sites to get more targeted visitors.