Celebrities have seen to influence people's mind. This is because most celebrities are envied by the public and are other people's role models. Therefore, whatever they say matters a lot to their fans. Hence they can influence the outcome of the election in a big way. They run the world.
Trump had so few "A" listers supporting him and he still won. Celebs can help by spreading the message to vote and by publicizing issues, but they can only effect the vote up to a certain point. If they had that much influence, Clinton would have easily won this time.
Celebrities do not affect the outcome of an election. If anything, they offer nothing but noise. If people follow what celebrities say and base their own votes on that, then our country is in extreme trouble. Use your own mind, think for yourself. Don't listen to mindless celebrities and worship them.
I think these kinds of endorsements are generally flimsy and don’t mean anything, but they appeal to the average person. If celebrity endorsements were really meaningful, Jeb Bush would still be in the Republican race and Hillary Clinton would have already wrapped up the Democratic nomination. Just a few voters make voting decisions based on celebrity endorsements.