It didn't worked because the onclick code is prefixed with "return" keyword, which will return after completing the first function, and won't execute the second function.
if your validation function is returning true or false then try this out -
Code:
<div id="formbuttons"><input class="buttonsubmit" id="btnsubmit" name="btnsubmit" onclick="if(formvalidate()) {wrs_trackclick('DCS.dcsuri=formsubmit', 'WT.ti=form submit','WT.dl=24'); return true;} return false;" type="submit" value="Send"/> </div>