MVC 5 HTML helper for client side validation for value not in model - validation

Question

I'm following the MVC tutorial here to add a search/filter textbox:
http://www.asp.net/mvc/overview/getting-started/introduction/adding-search
I've added the filter textbox to my page:
#using (Html.BeginForm()) {
<p> Title: #Html.TextBox("SearchString") <br />
<input type="submit" value="Filter" /></p>
}
How do I perform client side validation on the textbox to ensure something was entered?
When you automatically created the controller and views based on a model, it creates this handy HTML helper:
#Html.ValidationMessageFor(model => model.Name, "", new { #class = "text-danger" })
Can something similar be used for a value not in your model or do you have to add custom jquery/html?
Edit:
Thanks for the direction everyone. Just adding some more information now. I've created a new class in my existing model:
public class SearchItem
{
[Required]
[StringLength(100, MinimumLength = 5, ErrorMessage = "This is my test error message")]
public string SearchString { get; set; }
}
Then inside the controller, I've created a partial view:
[ChildActionOnly]
[AllowAnonymous]
public PartialViewResult Search()
{
return PartialView();
}
Then I've created a new Search.cshtml with:
#model App.Models.SearchItem
#using (Html.BeginForm())
{
#Html.ValidationSummary(true, "", new { #class = "text-danger" })
<div class="form-group">
<h4>#Html.LabelFor(model => model.SearchString, "Search:", htmlAttributes: new { #class = "control-label col-md-2" })</h4>
<div class="col-md-10 input-max-width">
#Html.EditorFor(model => model.SearchString, new { htmlAttributes = new { #class = "form-control" } })
#Html.ValidationMessageFor(model => model.SearchString, "", new { #class = "text-danger" })
</div>
</div>
<div class="form-group">
<input type="submit" value="Search" class="btn btn-primary" />
</div>
}
#section Scripts {
#Scripts.Render("~/bundles/jqueryval")
}
Then on my existing page, I add it with this:
#Html.Action("Search", "Items")
When I enter no text into the textbox and click the Search button, the page just refreshes and I get no client side validation.
My HTML looks like this:
<form action="/Items/Index" method="post"> <div class="form-group">
<h4><label class="control-label col-md-2" for="SearchString">Search:</label></h4>
<div class="col-md-10 input-max-width">
<input class="form-control text-box single-line" data-val="true" data-val-length="This is my test error message" data-val-length-max="100" data-val-length-min="5" data-val-required="The SearchString field is required." id="SearchString" name="SearchString" type="text" value="" />
<span class="field-validation-valid text-danger" data-valmsg-for="SearchString" data-valmsg-replace="true"></span>
</div>
</div>
<div class="form-group">
<input type="submit" value="Search" class="btn btn-primary" />
</div>