My Baby Is Missing And I Need Advice

We adopted a kitten over the weekend and a few days later our older cat ran away. He’s been gone 2 nights now which has never happened before. I’m positive it’s because of the new kitten. I am so sad and I don’t know what to do. I didn’t think this would happen. I really thought he would end up liking her and he hasn’t had to spend much time with her since we were keeping them separated to try to introduce them slowly.
Do you guys think I should leave the new kitten at my parents’ house for a few days to see if he comes back?

I’ve posted to our neighborhood website and Facebook and I’m putting up fliers today. I’ve notified some of our neighbors to be on the lookout for him as well. I’m so worried about him and praying that he comes back. He’s microchipped luckily and had a collar but I can’t help but think the worst.

I’m wondering if he thinks the kitten is gone if maybe he will come back. What do you guys think?

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Keep in mind that this may have nothing at all to do with the kitten - it may simply be that he had the chance/opportunity to go outside...and he took it.

But, if it will ease your mind at all and, if the kitten will be properly cared for at your parents' place, then just do it.
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So sorry that your older cat ran away. As early as it is in the process of having a new kitten in the house, she should be confined to a single room at this point. That being the case, I am not sure what benefit there would be in removing her from your house altogether. If she already has run of the house, you might want to consider going back to step 1 of the Introduction Process and place her in a room of her own.
How To Successfully Introduce Cats: The Ultimate Guide

In addition to what you have already done to try to find your cat, you may also want to notify local vets, shelters, rescue centers, SPCA, etc. as well. If they have fliers, they too can be on the look out when someone just might bring your cat in for a micro-chip check. And, call them often just to check if they might have heard/seen something (squeaky wheel gets the grease).

I would also put clothing/towels with both his and your scent on them outside. Some even place their cat's litter box outside. And, at least at dusk/dawn - if not more times - go outside with a bag/can of his favorite food/treats and shake it while calling him. You need to stay in place for at least 1/2 hour when doing this to allow him time to come to you.

See if there are any other tips in this TCS link.
Tips for finding a lost cat

MOST cats who run away are found, if they are indoor cats, hiding very close to home, although a really adventurous cat can range up to 3-5 miles from home! When you are out searching at dusk and dawn, be sure to carry a flashlight! That eye shine has given away many a cat's hiding spot. They favor small, dark places. And don't forget to look UP, in case he was chased up a tree and can't get down!