Auto complete box with multiple values in SharePoint Web Part using J query and SharePoint list web service

SharePoint 2010 Questions.

I am trying to create an auto suggesting text-box with multiple values in a SharePoint web part. i am using j query and SharePoint list web services to do it. I am just learning to do these stuffs but not getting a result. Any help much appreciated.

Following is the code. i am creating an alert to see if i get any data but it alerts a blank dialog

this is my latest code

var restServiceAddress = "/_vti_bin/ListData.svc/";
var listName = "Topics";
function split(val) {
    return val.split(/,\s*/);
}

function extractLast(term) {
    return split(term).pop();
}  

  $(document).ready(function () {


    $('#<%=input_title.ClientID%>').autocomplete({

        source: function (request, response) {
            $.ajax({
                type: "POST",
                contentType: "application/json;charset=utf-8",
                url: "" + restServiceAddress + listName,
                data: "{'Title':'" + request.term + "'}",
                dataType: "json",
                success: function (data) {
                    response($.map(data.d, function (item) {
                        return item.Title;

                    }))
                }
            });
        },
        focus: function () {
            return false;

        },
        select: function (event, ui) {
            var terms = split(this.value);
            terms.pop();
            terms.push(ui.item.value);
            terms.push("");
            this.value = terms.join(", ");
            return false;
        },
        minlength: 1

    });
});