my best advice would be that you need to take things SLOW and don't rush anything
you might run into a cop who would nail you for inappropriate behavior
or another member who would rat you out and get you dismissed from your gym, or worse.
INSTEAD....
Go slow. Choose the guys you are interested in. Smile, maybe say hello on a repeat visit to establish yourself as a "regular" guy and someone who he might see from time to time. Make eye contact- don't avert your eyes. Sit upright and strong, be confident about yourself. Keep an open posture- don't close your arms and look angry, and don't sit in the corner with your eyes closed, ignoring everyone in the room... remain "open" to social interaction.
On the first time seeing them, PLEASE don't uncover your towel and "WHIP IT OUT." Most guys are going to be nervous - and concerned that maybe you are underage and could be a liability. That's abnormal social behavior- and you almost NEVER know at a glance that it is welcomed by the other person(s) in the room. You will eventually grow to read other members- but sometimes even the best guess can be wrong.
Instead, win the trust over a few visits. Don't make your true intentions known. Maybe drop your towel and flash your tush as you get up to go to the showers- but innocently. Warm up to it. Wipe the sweat from your arms, chest, legs, and (with modesty) around the inside of your legs. Occasionally use the edge of your towel to wipe the sweat from your forehead- revealing your crotch momentarily. See if your actions are mirrored. If they are, things can slowly escalate.
The biggest thing to watch is the EYES. If he never looks over at you or if he doesn't return your gaze at all- or keeps his head looking at the floor the whole time- then he's not going to be your playmate, man. Don't try to get anything going, because he's not there with you. He's trying to be in the room by himself--- maybe feeling a bit self aware since he's mostly naked, covered by just a towel.
Instead, just like the advice above- here's how the game is played: look over, smile, look away. When he uses his towel to wipe his face, take your peek. Allow yourself to be seen looking at him- just for a moment. It's socially ok for you to notice when someone else is in the room- he won't freak if you notice him. That's just being gracious. You have to pay attention to what follows.
See if he looks you in the face. If he does and you feel that connection, return his gaze. Just like you're looking at other details in the room. Don't make him feel like you are staring or sizing him up. If he does look at you, notice your body, don't look away. Then look directly at his crotch and then back in his face- allow him to see that you are specifically looking at his crotch. If he's into it, it will go from there, or that might be too much and he might get up and leave.
Just make your movements one step at a time, like climbing the rungs of a ladder- to size him up and see if he is up for it. You'll know, and you'll make a friend. Don't rush it, and don't do anything overt without being fairly sure that it is welcomed action. Slow and steady is going to get you a more significant return in situations like this.