Not too difficult, actually.

The thing is that you have to put in more effort than when younger.

Proximity and constant contact is easy when you are young.

One of the things that made it easier in elementary/jr high/high school and/or university is that you were in classes every day or every other day with the same person for months. You see them on campus or buildings as you are walking around. Going to school is mandatory, so you will see the same people every day.

It's easy.

As an adult, it is not the same. But that is why office romances are so common. You are forced to see the same people every day. But there are other places. Some go to church for social contact, not necessarily worship. Or maybe worship is a 2 or 3 and social is 9 out of 10 in importance.

One solution is to go to groups with weekly meetings. Monthly is not frequent enough. I met a lot of cool people in a hiking group and a technical groups that I went to.

If you start your own hiking/walking group and get 10 or 20 people to attend, you will have a lot of friends, especially if you are the group leader. Leaders always get the attention of everyone - it's built into our DNA. You are the one who puts in the effort, gets people together, plans where you go to walk. You have to "market" the group. You also have to plan extracurricular activities - if you have a hiking group, every few months you can have a party at your house for your group, or BBQ or whatever.

Join weekly groups, or create a weekly group. That's the best way. If you just don't want to put in the effort, well, what can I say. You won't get together frequently enough to form bonds. It really just isn't possible, or maybe just not likely anyways. You want to increase probabilities, you need to meet with people weekly. I think creating the group is best.

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Here are some ways if you want to createyour own group to find and attract members:

Create a Facebook group or page and invite your friends to join and share it with their network.

Use other social media platforms such as Twitter, Instagram, or LinkedIn to promote your group and reach a wider audience.

Create a website or a landing page where people can learn more about your group and sign up to join.

Post flyers or posters in public spaces such as coffee shops, libraries, or community centers.

Attend local events and hand out flyers to people who might be interested.

Use word of mouth and tell your friends, family, and colleagues about your group and ask them to spread the word.

Ask local related businesses if you can post flyers or business cards in their establishment. Camping stores for hiking, computer stores for tech groups, etc.

Use online community platforms such as Meetup, Eventbrite, or Facebook Events to create and promote your group.

Create a group on LinkedIn and invite people in your industry to join.

Use Reddit to post about your group in relevant subreddits.

Reach out to local organizations or clubs and ask if they would be interested in collaborating with your group.

Use Craigslist to post about your group in the community section.

Attend networking events and conferences to meet new people and promote your group.

Create a hashtag for your group and use it on social media to increase visibility.

Use paid advertising on social media platforms such as Facebook or Instagram to reach a wider audience.

Partner with local newspapers or radio stations to advertise your group.

Use email marketing to reach out to people who might be interested in joining.

Attend local festivals or events and hand out flyers or business cards.

Use Google AdWords to target people searching for keywords related to your group.

Create a YouTube channel and post videos about your group to promote it.

Use influencer marketing by partnering with people who have a large following in your niche.

Attend relevant industry events and promote your group to the attendees.

Partner with local schools or universities to reach out to students who might be interested in joining.

Partner with churches and other types of places where people meet regularly.

Host a launch event or a meetup to introduce your group to the community and attract new members.