Please help quick! Should I reach out to her?

My deadbeat babydaddy hasn’t been in my sons life in 5 years. He dropped off the face of the earth after I told him I was pregnant. I haven’t been able to get into contact with him and child support can’t locate him. Finally through some deeper digging I found the mother of his first child. He’s in that boys life. Should I reach out and ask for his contact info or let her know that our kids are siblings in case she cares to let them meet?