With respect to the original question,
Is it illegal to create a foreign website that let users post their places of entertainment that they like ( including prostitution locations )
John is right in one regard -- that it is legal to talk about prostitution in the US (at least it is now). However, prosecutors often don't give a shit what the First Amendment says -- they want to satisfy their superiors, further their career, please their pastor, or simply don't believe in their oath of office. Do a Google search for "Mary Beth Buchanan" for a prime example.
If you are posting a website with links to prostitution or gambling related activities, you are walking on dangerous ground. I'm sure that everyone is aware of the Kentucky gambling domains fiasco -- at least one of the websites in question was doing nothing more than providing a link to other websites. In Pennsylvania (under Ms. Buchanan's authoritah) people have been prosecuted (and convicted) for a) writing about sex acts without actually performing any of the acts (defendant pled out because she was agoraphobic and the plea deal was for house arrest), b) selling "water pipes" (Tommy Chong), and c) selling the "whizzinator" (look it up).
So, the short (and correct) answer is that we still have a Bill of Rights in the United States, so what you propose should be protected by the First Amendment (and you might be immunized under 47 U.S.C. s 230). The more complex answer is that you could find yourself hauled before some nut-job psycho-religious unethical piece of shit prosecutor who doesn't care what the Constitution says -- and you'll find yourself making some difficult choices.
Before you venture into such a foray, get some help from an attorney who specializes in this kind of thing.