"LOL" is the signular form, and "LOLZ" is simply the plural.
Meaning "lol's" or more than one "lol".
Adding a lowercase "z" at the end (Proper form, LOLz, or LoLz to switch between capitals and lowercase as is commonly done by a number of prepubescent horny teens, namely girls) does not necessarily add another word to the acronym. Just like if I were to write to you about "STDs", I would not be talking about Sexually Transmitted Disease Succotash, but rather multiple Sexually Transmitted Diseases.
AbErCrOmBiEhOn121: LoLz!!!1 ur lyke soooo rite, shes lyke such a hoe bag! but i luv u, ur 2 good 2 b 4gotn!
QtPiEGuRlyGuRl24: lolz!!1 i luv u 2! lez go shoppin!
AbErCrOmBiEhOn121: aight honee lemme juss get mah REEL coach bag
QtPiEGuRlyGuRl24: shut da fuc up slut!
QtPiEGuRlyGuRl24: lolz! jkjk!
Yeah you get my point...
In leet speak, plurals are generally denoted by a 'z' instead of an 's', so lols becomes lolz.
2. lolz (v.) - A leet corruption of lols
Treating lol as a verb (to lol), the he/she/it conjugation of lol in the present indicative tense is 'lols', (i.e. I lol, we lol, he lols).
Using the leet practice of replacing 's' with 'z', this is corrupted to 'lolz' (I lol, we lol, he lolz)
2a. "N af7r 7h47 he lolz r33lly h4rd"
2b. "And after that he lolz really hard"