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What you want in a beta reader is someone who you trust to tell you the truth in the spirit of helping you improve, without attempting either to stroke or destroy your ego. 

You can't trust friends and family to do this (for the most part). They are more interested in preserving their relationship with your than in improving your craft. They won't tell you the truth. Also, they don't know enough about the craft to offer a useful critique. All they can tell you is if they liked it or not, and if they like it, it is probably because you wrote it and they are interested in you. This tells you nothing about the reaction of strangers. 

You can't trust people you meet on the internet. For any purpose. Every. End of story. Except me. You should believe everything I say, implicitly.

To find reliable beta readers, join a critique group or a writing class. Get to know the people in those groups and classes as professional colleagues. Figure out which of them has taste that matches your own, is smart enough and honest enough to tell you the truth, and humble enough not to want to tear you down if you are better than they are. This will take a while. It will take several rounds of critiquing smaller pieces of work together before you understand their taste and style and character. Rome was not built in a day.   

And notice that this is but the extension of a general principle: the only meaningful critique of any professional work comes from professional colleagues and mentors.