How to connect with other makers?

The most important thing is to ask yourself, why do you want to connect with others. If you're looking for advice or someone to talk to about your business and problems you face running it, you should look for a local mastermind or entrepreneurs community. Organize regular meetings, and regularity is very important here, because most business problems are not things, that you can solve right away. Be careful though to find people, that have a business of your size or a little larger. Because if you're running a company of 10 people, and you'll try to talk about your problems with someone who's got 100 people onboard, his advice will most probably not be of much value for you anymore, since he's facing totally different problems, than you are, and he does not really care to meet with you regularly to coach you. I do not see it really possible to find this kind of advice and mastermind group online. But if you're looking to test your ideas, mvp, ask opinions, instead of other makers you should be looking for your potential customers, and talk with them. Other makers will not help you much in terms of customer needs.

Twitter Communities but not a lot of engagements. There are FB groups, too, but just lots of links and announcements. Had a client before building on Instagram (because his target audience is there) and found his beta testers there and build his FB group. I can't tell yet the best platform but #buildinpublic has a lot of potential when used correctly along with listing platforms like product hunt.

This might be an unpopular opinion, but there aren't a lot of good communities online that I've found (Product Hunt is good though). I would recommend applying to an accelerator or finding a local co-working office to go to to connect with people. I think a lot of makers are busy making and promote their products in online communities rather than help.

Friends and past co-workers you got along with very well are probably one of the best sources to tap into