Being alone amid the crowd is something that happens more often nowadays: you see people every day with their phones, chatting on "whats app" and not trying to socialize with anyone near them. They don't want to leave their comfort zones and it is too bothersome for them to get to know someone that they don't know anything about .
And then, they create a wall around themselves to avoid meeting  someone new, which would disturb their "safe zones". They would rather live in their closed world, where no one can create a social bond with them; even if someone interacts with them , they will not be reached . They are living in a social media world in a state of solitude amid the crowd.
: not necessarily wrong, but it probably did not sound good the way it was originally written.Bold
: problems with grammar, vocabulary or spelling.Recommendations
 Shouldn't your text have a title? When in doubt, provide one.
 The way you started your sentence was not very good, so I changed it slightly.
 This extract sounds redundant to me: "(...) start to know someone that they don't know anything about
". I recommend you to replace it.
 Find out the difference between know and meet here: know-x-meet-x-get-to-know-qual-a-diferenca-t10691.html
 I don't know exactly what you meant by "social contact
", but I assumed it had an idea similar to interaction
 I rewrote most of your sentence, because the second paragraph has the same ideas of the first one, only phrased in a different way.
 Solitude is an uncountable noun, so you may not use it as in the following extract: "(...) in a solitude amid the crowd"
. Only if there were a countable noun there you could use such structure.
 A last piece of advice: read! The only way to write properly is by reading content from different sources, such as magazines, newspapers, online blogs, books, etc. Find out what amuses you the most and start reading for ten minutes a day; the results will amaze you.