how to add font-size toolbar in tinyMCE?

All you need to do is to add fontsizeselect to your toolbar config param:

toolbar: "sizeselect | bold italic | fontselect |  fontsizeselect",

Update:

tinymce.init({  fontsize_formats: "8pt 10pt 12pt 14pt 18pt 24pt 36pt"});

This may be of use for perspective. Below is my TinyMCE init JS code which includes the option for font type and size.

tinymce.init({    selector: '#articletextarea',    plugins: [        'advlist autolink lists link image charmap preview hr anchor pagebreak',        'searchreplace wordcount visualblocks visualchars code',        'insertdatetime media nonbreaking table contextmenu directionality',        'emoticons template paste textcolor colorpicker textpattern imagetools codesample'    ],    toolbar: 'codesample | bold italic sizeselect fontselect fontsizeselect | hr alignleft aligncenter alignright alignjustify | bullist numlist outdent indent | link image | insertfile undo redo | forecolor backcolor emoticons | code',    fontsize_formats: "8pt 10pt 12pt 14pt 18pt 24pt 36pt",    height: "350",    menubar: false});

theme_modern_font_sizes: "10px,12px,13px,14px,16px,18px,20px",font_size_style_values: "12px,13px,14px,16px,18px,20px",toolbar: "insertfile undo redo | fontsizeselect |