Where can I advertise a video site for adults?

Are you looking for payment or free?

Free methods:
Social media:
Twitter
Tumblr
Pintrest (be careful)
Sex.com
reddit
pornterest
PinSex
Adult space
Pornstagram
Uplust
TheAdultHub

Important tube sites:

Upload videos with watermark and add a link in the description and profile in:

xvideos
xhamster
pornhub
Myvidster
motherless
youporn
txxx
nuvid
flyflv
machomoe
fucking1

Version of the Android / iPhone application of your website

Mikandi.com
Lazeeva
Aptoid
Getjar
app-eshop.xxx

Web 2.0 / Free Sites
EasyXTubes
EasyXblogs
Pornfinder

kinky-blogging.com
pornlivenews
pornblogspace
sensualwriter.com
venusblogger.com
adultblogspot
blogsbugs
www.jizzy.info
freeblognetwork.com
pornmeme .com
adultwordpress.com
isanadultblog.com
pornspaces.com

URL shorteners:

Linkbucks.com
B.eave.rs
Adult.xyz
x18.eu

Traffic exchanges that accept adults:

10khits.com
Otohits.com
Hitleap.com
Pandabot
Armybot.net

(The above is not an exhaustive list, but there are many free resources to start, the same applies to the following paid sources)
Paid promotion of adult sites:

Adult.xyz
b.eave.rs
Popcash
popmyads
Popwin
Popearn
poptm
adxxx
adnio
popxxx.net
pinvert
hills
ad maven
exoclick
scrub
juicy
advertising
creamyads

Froggyads
arteebee

(Just do NOT use PopAds.net. That guy is a scammer.) He stole the $ 25 from me. I deposited the funds, immediately closed my account, citing a false "multiple account" excuse when I had never had any prior contact with that company, never I ran my campaign or they returned my funds despite repeated support tickets (no response) … Draw your own conclusions, but I think everything "received money, did not provide service and did not work, saved money and did not return emails "it explains everything quite well …)

I hope this helps as a starting list – this was only part of my head (all this I used / bought personally by the way)