I don't think there's a universally accepted way to deal with this, but probably the least controversial way is to just not bother marking the accusative. The meaning is usually clear from the context anyway. In number 1 and 3 of your examples the meaning is clear because the subject of the phrase is marked by the lack of the n suffix so the other unmarked part can only be the object. For number 2, you can assume the default subject-verb-object word order to get the meaning.
Another option is to force the ending on onto the word separated with a hyphen:
Mi ŝatas Facebook-on
There are at least two experimental ways to express the accusative with a preposition. One of these is to use je:
Mi ŝatas je Facebook.
I personally find this usage quite clumsy so I would recommend against it.
Another is the preposition na which is a proposal for a preposition to explicitly show the accusative. For example:
Mi ŝatas na Facebook.
It can be used in other cases as well to solve the ambiguity in de with a verb-like noun:
Temas pri manĝo na kokoj.
However this word is not widely known and often when using it you will probably have to explain yourself and end up with a tedious debate about whether reforms are acceptable in Esperanto rather than whatever conversation you were trying to have in the first place.
I personally find Esperanto-ising the words an acceptable solution (eg, mi ŝatas vizaĝlibron) but as demonstrated by makis' answer that is not without controversy and it isn't always possible anyway.