Omar Mateen on Dating Apps: Penis Pics to Guys, But Also Scoping Out Women

There are mounting claims that Omar Mateen was gay and looking to hook up on apps and in clubs -- but it appears he was also actively hitting on women ... a strong sign of a possible struggle with his sexuality.

Cord Cedeno says he connected with Mateen a couple years ago on Grindr, but it was hardly titillating. Cedeno says Mateen -- whose profile was a pic of him in a tie -- would only say "Hi" over and over. He says he eventually blocked Mateen, but knows 4 friends who say the Orlando murderer remained active on other apps.

He says Mateen used Adam4Adam to send shots of his penis to men -- but never showed his face. Cedeno says he has no knowledge Mateen was ever successful in hooking up with a man.

On the other hand ... a female user on Plenty Of Fish says Mateen reached out to her 18 months ago. She says he was "nice, normal ... mentioned he had a child, but said he was single and looking for a good woman to marry."

She told us Mateen never said anything about being into men, but did rant about Islam and the Quran ... saying people misunderstood his religion. She says he wanted to meet face-to-face, but she too blocked him because he seemed "emotionally unstable."