How old are you?
Here is what you do to sniff panties and I'll give you various scenarios from my successful hunts
1) I assume they are in school. When they go to school drop by the house. This gives you an opportunity to sniff through soiled panties (tbh I always preferred going for the freshest ((if you catch my drift)) pair of undies because chances aren't you aren't sniffing dried chad ejaculate because that is gay. you want prime vagina scent that is all vagina) from the laundry or you can head into their room super fast and sniff some clean ones. If you look into her drawer and you see 10+ of the same type of underwear you can steal a pair. The Mom won't realize one pair missing and will assume her daughters bled all over one and threw them away. Innocent enough. And the daughter obviously isn't going to notice because she isn't the one paying for them. DO NOT: I REPEAT DO NOT STEAL UNIQUE PANTIES!!! If her favorite panty has a fucking coca-cola bear on it and there is only one panty with that in her drawer and you steal it you WILL get caught. Or at the very least highly suspected forever more. If you need to plan ahead then do so. Leave sometimes inoqulous like a pair of airpods. "Ah shit cousin I left my airpods in your room. I'll get them next week" or something like that. Then go when she is out because you have an excuse.
2) It doesn't need to be underwear. Bras work just as good and sometimes even better. Boob sweat smells heavenly. Even better when its from a girl with really perky boobs. And all girls under a certain age all have the perkiest of boobs. Do with that information what you will. Socks smell heavenly when she has worn them all day. You can even sniff her yoga pants or any tight clothing. Where I live it is incredibly hot. Tons of girls are going out and swimming and in bikinis and swimwear. Typically these are also in the laundry or hung up to dry somewhere. You can also smell that for a few good sniffs.
3) Plan ahead for various circumstances. She is 16 and 17. I assume they can drive. If they are regular girls and of driveable age (the best age) then don't eat before you go there. Say something like, "Man. I could really go for some McDonalds right about now." As teenage girls they will be giddy and jump at the chance to go out and buy fast food. I don't care what fucking restaurant it is. Just say something they like. Offer to pay if need be. Once they go out and are driving to buy the food that gives you 20-30 mins to bust real fast before they come back. Extra time can be added if you order from an actual restaurant like idk Olive Garden or something then you get 35-50 minutes. With that amount of time you can actually put their panties around your cock and please yourself that way.
4) This is a bit trickier but if possible go through her phone. All teen girls are whores these days and even if it is just for "artistic" uses (i.e. bullshit) she will have nude selfies on her phone. It would take too long and tricky to link them to your phone. It is risky to send them to your phone. What you do is find a forum or some bullshit chan site (like not 4chan but a loser version) and upload them there. The Sewers or something similar where things are posted and deleted quickly would be optimal. Nobody would even notice. You post them on that site and then save them through your phone that way there is no trace. Now you have fap material for as long as you aren't stupid.
5) All teen girls have sex toys and/or objects they use as sex toys. Figure out what that is. My cousin had a purple vibrator. I sucked on it and spit on it and came all over it and lubed it up with my cum. So fucking hot thinking she unknowingly stuffed it in her pretty pink pussy all the while she's slicking herself off with her cousin's manhood.
Happy hunting my friend! Please report back with your DETAILED indevures
PM me when you do. I don't want to miss it. You better not pussy out because I didn't write this for nothing