Sharepoint 2013 search auto suggest using api.

 Use the below snippet for SharePoint 2013 search suggest.This will only work for authenticated users not for anonymous users.

 <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
<asp:TextBox ID="txtSearch" runat="server"></asp:TextBox>
<script type="text/javascript" src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script type="text/javascript" src="http://code.jquery.com/ui/1.10.3/jquery-ui.js"></script>

<script type="text/javascript" >
        var j$ = jQuery.noConflict();
        var siteCollUrl = "";
        SP.SOD.executeFunc("SP.js", "SP.ClientContext", function () {

            var clientContext = new SP.ClientContext.get_current();

            var site = clientContext.get_site();

            clientContext.load(site);

            clientContext.executeQueryAsync(Function.createDelegate(this, function () {

                siteCollUrl = site.get_url();

            }))

        });


        function GetConfigValue() {

            if (siteCollUrl.charAt(siteCollUrl.length - 1) == '/') {
                siteCollUrl = siteCollUrl.substr(0, siteCollUrl.length - 1);
            }
            return siteCollUrl;

        }

        function EncodeString(input) {
            input = input.replace(/&/g, '&amp;');
            input = input.replace(/</g, "");
            input = input.replace(/>/g, "");
            input = input.replace(/'/g, "");
            return input;
        }

        j$(document).ready(function () {

            var termTemplate = "<span class='ui-autocomplete-term'>%s</span>";

            j$(document.getElementById('<%=txtSearch.ClientID %>')).autocomplete({
                source: function (request, response) {
                    j$.ajax({
                        url: GetConfigValue() + "/_api/search/suggest?querytext='" + EncodeString(request.term) + "'&fprequerysuggestions=true&fhithighlighting=false",
                        method: "GET",
                        headers: { "Accept": "application/json; odata=verbose" },
                        success: function (data) {
                            var result = data.d.suggest.Queries.results;
                            jsonObj = [];
                            var arrayLength = result.length;

                            for (var i = 0; i < arrayLength; i++) {
                                var suggession = result[i].Query.replace('<B>', '<span class="autosuggest">').replace('</B>', '</span>');
                                item = {}
                                item["label"] = result[i].Query;
                                item["value"] = result[i].Query;
                                jsonObj.push(item);
                                //Do something
                            }
                            response(jsonObj);
                           
                        },
                        error: function (result) {

                            alert("Un expected error.");
                        }
                    });
                },

                messages: {
                    noResults: '',
                    results: function () { }
                },


                minLength: 3
            }).data("ui-autocomplete")._renderItem = function (ul, item) {
                var term = this.element.val(),
                    html = item.label.replace(term, "<b>$&</b>");
                return j$("<li></li>")
                    .data("item.autocomplete", item)
                    .append(j$("<a></a>").html(html))
                    .appendTo(ul);
            }



        });

    </script>