how do i be more likeable?

i come with the full package; i am a very shy and introverted person, but i also have a hard time expressing my thoughts and i end up stuttering. it takes me too long to think of words to fit my sentences, so my friends mostly end up talking over me most of the time. i do everything to be a good friend; listen to their troubles, respect their boundaries.... i just don't get why i tend to end up as the "left out friend", speaking from experience. in most friend group situations, i am the one left out and made fun of. i think it has to do something with myself and my likeability. do i have to be funny? what will it take?