In answer to your question I think the reason you don't get responses is because responding to property requests is almost always a fruitless endeavor. I get emails/leads every day from people on Trulia and then when I return their email or call they don't reply. After a point replying seems futile.
I strongly suggest you call an agent and if they don't pick up leave a detailed message. By "detailed" I mean more information other than your desire for the Realtor to call you back. We get telemarketers calling us all day long and they tend to leave generic "please call me back" messages.