Does the name Lola del Rio ring a bell? …No? Lollipop girl from the cover of GTA 4? Theeeere we go. She's fairly popular despite pretty much no one knowing her name or very much about her (besides the fact that she's a prostitute, which is surely inconsequential), and many fans took to message boards the world over for help finding her in the game. Sadly for budding Johns out there, this lady's unavailable. Wait, no, there's a better word. Non-existent. That's the one.
Admittedly, some of the confusion falls on Rockstar for this one, since a file on Lola does appear in the Liberty City Police database. Within, players can find details of her arrest record, as well as information on her usual hangouts. However, like many of the fun/outrageous/downright bizarre tidbits inserted into GTA games, Lola doesn't actually exist, and there is nothing to be found if you go in search of her. Maybe she turned over a new leaf, or really did become an actress like she always wanted. Good for you, Lola. Follow your dreams.