Hey This Javascript work fine for me
<pre lang="cs">//for serching gridview on keyup
function Filter(Obj) {
var grid = document.getElementById('cntPlcHolder_gvDisplay');
var terms = Obj.value.toUpperCase();
var cellNr = 0; //your grid cellindex like name
var ele;
for (var r = 1; r < grid.rows.length; r++) {
ele = grid.rows[r].cells[cellNr].innerHTML.replace(/<[^>]+>/g, "");
if (ele.toUpperCase().indexOf(terms) >= 0)
grid.rows[r].style.display = '';
else grid.rows[r].style.display = 'none';
}
}</pre>
//calling of function
<input type='text' onkeyup='Filter(this);' id="txtSearch" class="SmallTextBox" runat="server" />
Best Luck