JSFiddle - React, Tailwind, and code Playground

HTML

<input type="search" id="search" class="input-s search" onkeyup="SearchFunction()" placeholder="Введите компанию">
 
 <div class='notfound'></div>
 
 <ul id="offerfilters" class="offerfilters">
 <li class="searchel filter-block-m"><a class="searchela">ВК</a></li>
 
 <li class="searchel filter-block-m"><a class="searchela">ФБ</a></li>
 
 <li class="searchel filter-block-m"><a class="searchela">Инстаграмм</a></li>
 </ul>

JavaScript

function SearchFunction() {
    // Declare variables
    var input, filter, ul, li, a, i;
    input = document.getElementById('search');
    filter = input.value.toUpperCase();
    ul = document.getElementById("offerfilters");
    li = ul.getElementsByClassName('searchel');
    

    
    // Loop through all list items, and hide those who don't match the search query
    for (i = 0; i < li.length; i++) {
        a = li[i].getElementsByTagName("a")[0];
        if (a.innerHTML.toUpperCase().indexOf(filter) > -1) {
            li[i].style.display = "";     
        } else {
            li[i].style.display = "none";
        }
    } 
    
/*     if([...li].every(element=>element.style.display=='none')){
      document.querySelector('.notfound').textContent = 'результатов нет'
    }else{
          document.querySelector('.notfound').textContent = ''
    } */
     document.querySelector('.notfound').textContent = 
     		[...li].every(element=>element.style.display=='none')? 'результатов нет' : ''
    
}