Throughout the show, they just lie about having Friends who are outside of the core group. They talk about other people, even bring up names, but they never materialse. The only time was when Monica and Phoebe's old friend shows up. None of their other friends:

- Attended Ross' wedding

- Phoebe's wedding

- Monica & Chandler's Wedding

- Rachel's leaving party

Very much a case for /r/thatHappened