I'm sorry you're going through a crap time op. Heartbreak is the shitiest feeling.
I'm going to go against the grain here and i don't mean to sound horrible but I don't think you should use POF'.
I get you need an ego boost and that you're feeling down but that is all part of getting over something. Masking it and flirting with strangers isn't going to help you move on.. it will be a distraction but I'm all for throwing yourself into Heartbreak, if that makes sense.
What I mean is the shitty bit, the hurt has to be felt, it's all part of the process. You have to go through it to heal.
I don't think it's a nice thing to start anything with someone that is looking to meet someone when you aren't. POF is full of time wasters but there are some genuine men just looking for a relationship on there too. Using a dating site to boost your confidence, to me, feels like playing with people's feelings. It would be horrible to start chatting to someone who takes the time to chat to you, ask you questions, flirts etc when you have no intention of ever meeting them. We read lots of threads on here about women who suffer at the hands of men who do that and the advice is always the same 'you get lots of time wasters on POF' or 'He's just using you for an ego boost' Dont be a female version of one if those people op, you sound too nice for that.
Yes you could forewarn by explaining your situation straight off but I am concerned about doing that. Any genuine nice man looking for a relationship wouldn't even consider starting a conversation after being made aware of your intention. I am concerned that leaves you open to the POF daters who have other agendas and I think at the moment your emotional state makes you too vulnerable to cope with that. I would hate you to get caught up in something that could be unhealthy for you right now.
Finally, and I'm aware this sounds like the biggest cliche ever, but it's one of the hardest most important lessons I've learned over the last year, you need to find a way to internally validate yourself. It's ok for people to say nice things to You, for strangers online to compliment you but if you don't feel it internally it won't make a jot of difference to how good of bad you feel.
You need to get to a place where you believe those nice things, then others people's compliments won't be necessary. Learning to gain and be the provider of your own self worth is the most important thing to possess. Unfortunately turning to others for that at this vulnerable stage is not ahealthy need to have.