By connecting with people, talking to them, building momentum, and investing enough time to explore goodness of fit. Don't be in haste to onboard one as you would encounter too many "Yes-Sir" and "Me-Too" kind of guys. But, in a long run it's pragmatic thinking and synchronization of vision that matters. Otherwise, either you or your partner will end up sitting back home,trying to establish everything around cocooned comfort of home than in right market.
Use professional social platforms like Clarity etc to scout for right people. Otherwise, advises are always free!!
Finding a co-founder is almost like finding The One, but as Anna from Frozen learnt, you don't marry someone you just met. You need a relationship, a history together or even some mutual friends.
Like in dating, prince(s) charming doesn't have to answer a "list of criteria" in order to be a goof match, but he or she must have complementary sides in his or her skills (and preferably personality as well) or there is a small chance to have a synergy in you two building a company together.
Now that you know all this, start by looking at your friends, and at your friends friends. Can any of them be the right fit? If not, there are a lot of Meetups and other events that declare that they are co-founders "matching events". look for them and start dating. It is not idle but can be successful.
another way, that in my opinion is more risky, is post am ad on LinkedIn and in the right groups on Facebook, you will find great people there, but you will have to work harder on building your relationship, as personal relationship between the partners is not only very important, it's vital.
It's not easy. But first, ask yourself why you need a partner. In most cases you don't "need" one. If you need help with your start-up, find a mentor. You can often just pay the mentor per hour or give them some share in your business if you are short on funds. This approach is usually better than finding a partner. Partnerships are typically formed among friends, colleagues, etc. To me, it seems like you just need some general help/guidance and not a partner.
Feel free to contact me and provide some information about your start-up. Depending on what you are doing, I may be able to help you.
Finding a great partner in business i much like finding a great partner in life. It takes time for both of you to know and understand each other. Rushing in because it's the thing to do is a recipe for disaster. Make sure you have the similar world view, values and vision for the future. Working on projects together is a great way to "date" - get to know a prospective business partner. I'd recommend it as part of the due diligence for anyone looking to form a legal partnership. As one entrepreneur shared with me "I've been through a divorce and a break up with a business partner. The divorce was easier".