There are two parts to this: work and your local community.
For work, you're not going to do it alone. Someone on the HR side (or just general management, if the company is still quite small) is going to have to be a willing sounding board for remote employee concerns.
On the social side, this might be supporting a policy (as Mapbox did, maybe still does) of flying remotes to the holiday and other big parties, as well as, if able, just having them in every month or two to work alongside the non-remotes and make those connections. When I first started, I'd fly from Portland to DC for a week every 6-8 weeks. It helped that I lived in DC prior for five years (before Mapbox), so it felt like a natural connection.
On the technical and process side, we had a policy of things not existing (or not existing properly) unless they were in written form. This included decisions, context, back-and-forth reasoning, announcements, etc. We used GitHub for non-code "tickets" this way, almost like an internal blog and topic-focused discussion forum. This broke down in later years, but even to the scale of dozens of people was a great way to make sure that being 3,000 miles away and three hours "behind" wasn't as isolating.
For the local community part, go to meetups. Organize a weekly/biweekly social gathering with likeminded friends or peers. Work in coffee shops or other places out of the house. I found that I went stir crazy when I first started remote, because I wouldn't leave the house and needed some human contact. Placing all of that expectation on your employer and not on yourself is unreasonable. It takes effort.