"I noticed him when I was at Colchester and he was playing for Tranmere, so I have known about him for about 12 months," Pirates boss John Ward told the club's official website.
"He has also played for Leyton Orient, so although he is only 19 he does come with experience of the lower levels.
"He is a big lad and a line leader. He is what you would describe as an old-fashioned centre-forward, and he has goals in him, which is obviously important.
"I have said before that I have strikers here who need some help over the next 19 games, and I think Ryan's presence can provide what we are looking for and take some of the pressure off."