Searching is an art and a science and the Ask Patents format is not suitable for a complete tutorial. I can get you started. Google patents is the easiest patent search engine to use for a beginner. It also has the option of searching in google scholar.
I crudely typed - "social network" upload video audio image chat - in the search box. It brings up a list of granted patents and patent applications from a variety of countries. To narrow it to just actually granted patents, scroll down and see a selection on the left where you can chose STATUS and set it to GRANT. One example I is see is US8572493B2 Mobile device messaging application.
It involves the elements you mention but its claims are very specific. Very broadly speaking, you can get a patent for a particular combination of features that have a particular relationship to each other, like this person did. To look for other similar things, scroll down to see that google provides hyperlinks to patents this document may have referred to, to patents that might have referred to this patent, and now also to things google's algorithm thinks are similar.
Following these links can give you a reasonable view of the patent status of the field. Remember that only granted patents can keep you from building something but everything is relevant in keeping you from patenting your inventions.