If you are serious about finding someone with similar kinks, before I point you anywhere: 1. When you create a profile, be authentic. People want to connect on more than kinks too.
2. Your profile pic should be something more than a dick pic if the site allows for them.
3. Be patient. Online communities slant heavily towards straight men. Do not get frustrated. That is not attractive.
4. Be genuine in your messages. No one wants to read "dO U mEsS?" for the 30th time.

Now, you have Reddit options. See the sidebar for r/ABDLPersonals and r/LittlePersonals. If your kinks vary outside of this fetish, try some of the BDSM personals as well.
Then there's always Fetlife - try these groups:
https://fetlife.com/groups/15851
https://fetlife.com/groups/12964
https://fetlife.com/groups/2663
then search for others based on the exact dynamic you are looking for.

Are there munches or Little events in your area? Attend them. You'll have to look for those. I am a member of the Ageplay Atlanta fetlife group, and they post about their munches there.

Go solo to conventions, but with the purpose of having fun and meeting new people! There's Capcon and others out there. Just don't go with the intention of shacking up and giving off weird vibes. People are much more inclined with meet the real you.

Beyond that, there is DateCGL.com, personals on DailyDiapers.com, and some may recommend Alt.com, but I found that full of spammers. You could also try putting ABDL in your Tender or Bumble profile if you were bold enough.